United States v. Jason Alexander Phifer ( 2018 )


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  •            Case: 17-10397   Date Filed: 09/21/2018   Page: 1 of 30
    [PUBLISH]
    IN THE UNITED STATES COURT OF APPEALS
    FOR THE ELEVENTH CIRCUIT
    ________________________
    No. 17-10397
    ________________________
    D.C. Docket No. 6:16-cr-00024-GAP-GJK-1
    UNITED STATES OF AMERICA,
    Plaintiff-Appellee,
    versus
    JASON ALEXANDER PHIFER,
    Defendant- Appellant,
    ________________________
    Appeal from the United States District Court
    for the Middle District of Florida
    ________________________
    (September 21, 2018)
    Before JORDAN, ROSENBAUM, and DUBINA, Circuit Judges.
    ROSENBAUM, Circuit Judge:
    Case: 17-10397      Date Filed: 09/21/2018     Page: 2 of 30
    There’s no easy way around it. We’re just going to have to science the heck
    out of this case.1 And when we’re done with that, we’re going to have to law the
    heck out of it.
    Defendant-Appellant Jason Alexander Phifer was convicted of possession
    with intent to distribute a controlled substance, in violation of 21 U.S.C. §
    841(a)(1) and 21 U.S.C. § 841(b)(1)(C). The substance involved was ethylone.
    But as it turns out, ethylone constitutes a controlled substance—and Phifer
    was therefore convicted of an existing crime—only if ethylone is a “positional
    isomer” of butylone. Phifer says it’s not. To support his position, he urges that
    “positional isomer” means what he characterizes as the scientific term of art. The
    Drug Enforcement Administration (“DEA”) disagrees and contends that its
    regulatory definition of “positional isomer” governs, and even if it doesn’t,
    ethylone is a positional isomer of butylone under other scientific definitions. If the
    DEA is right that the regulatory definition necessarily governs, Phifer’s conviction
    stands. But if not, we must set aside Phifer’s conviction.
    After careful consideration and a crash course in organic chemistry, we
    conclude that the DEA’s regulatory definition of “positional isomer” does not
    unambiguously apply to the use of that term as it pertains to butylone and ethylone
    1
    We paraphrase Matt Damon’s character, Mark Watney, from The Martian (2015). See
    The Martian Quotes, IMDb, https://www.imdb.com/title/tt3659388/quotes (last visited Sept. 20,
    2018). The movie, in turn, was based on the book of the same name by Andy Weir.
    2
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    in this case. We therefore vacate Phifer’s conviction and remand for further
    proceedings consistent with this opinion.
    I.
    The Controlled Substances Act, 21 U.S.C. §§ 801-971 (“CSA” or “Act”),
    established five schedules of controlled substances, which the CSA regulates or
    prohibits. Touby v. United States, 
    500 U.S. 160
    , 162 (1991); see 21 U.S.C. § 812.
    The Act assigns to the Attorney General the task of adding substances to the
    schedules. 
    Touby, 500 U.S. at 162
    ; 21 U.S.C. § 811(a). But before the Attorney
    General may do so, he or she must follow certain procedures, including engaging
    in notice-and-comment rule-making, that typically require six to twelve months to
    complete. 
    Touby, 500 U.S. at 163
    ; see 21 U.S.C. §§ 811(a)-(c), 877.
    Because of that time lag, by the time a specific chemical formulation of a
    given drug was scheduled, people were able to design and sell drugs that behaved
    similarly to that substance but differed slightly in chemical composition, without
    risk of criminal liability. 
    Touby, 500 U.S. at 163
    . To address this problem,
    Congress amended the CSA to allow the Attorney General to place a substance on
    a schedule on a temporary basis when the Attorney General deems it “necessary to
    avoid an imminent hazard to the public safety.” 
    Id. (quoting 21
    U.S.C. § 811(h))
    (quotation marks omitted). Under this process, within thirty days after a new drug
    3
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    is identified, a new drug can be added to a schedule on a temporary basis. 
    Id. at 164.
    The Attorney General delegated to the DEA the power to add drugs to the
    schedules—including the power to schedule controlled substances on a temporary
    basis. 
    Id. (citing 28
    C.F.R. § 0.100(b) (1990)). Under this authority, in March of
    2014, the DEA Administrator issued an order temporarily designating butylone (1-
    (1,3-benzodioxol-5-yl)-2-(methylamino)butan-1-one) as a Schedule I controlled
    substance.2 79 Fed. Reg. 12,938-12,943 (Mar. 7, 2014). Substances qualify for
    Schedule I if they have a “high potential for abuse,” “no currently accepted
    medical use in treatment in the United States,” and no “accepted safety for use of
    the drug or other substance under medical supervision.” 21 U.S.C. § 812(b)(1).
    Butylone is a synthetic cathinone3 and acts, among other ways, as a hallucinogen.
    See 79 Fed. Reg. 12,938; Synthetic Cathinones (“Bath Salts”), Nat’l Inst. on Drug
    Abuse,      https://www.drugabuse.gov/publications/drugfacts/synthetic-cathinones-
    bath-salts (last visited Sept. 20, 2018).
    2
    On March 1, 2017, the DEA added butylone to its permanent Schedule I. 82 Fed. Reg.
    12,171-12,177 (Mar. 1, 2017). Because this occurred after the events in Phifer’s case, we
    analyze Phifer’s case under the law as it applies to drugs temporarily placed on the schedules.
    3
    Cathinone is a substance found in the khat plant. Synthetic Cathinones (“Bath Salts”),
    Nat’l Inst. on Drug Abuse, https://www.drugabuse.gov/publications/drugfacts/synthetic-
    cathinones-bath-salts (last visited Sept. 20, 2018). Naturally occurring, it has mild stimulant
    effects. 
    Id. Synthetic cathinones,
    also known as “bath salts,” are human-made versions of the
    natural product, and they can be much stronger and more dangerous. 
    Id. 4 Case:
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    The list of drugs on Schedule I appears at 21 C.F.R. § 1308.11.4
    Subsections (b) through (g) of this regulation identify substances placed
    permanently on Schedule I.             See 21 C.F.R. § 1308.11(b)-(g).             Among these
    substances permanently listed, certain hallucinogens are set forth at subsection (d).
    Meanwhile, substances temporarily listed—which may include all types of drugs,
    including hallucinogens—are identified at subsection (h).                    See 21 C.F.R. §
    1308.11(h). At the time relevant to Phifer’s case, butylone, along with “its optical,
    positional, and geometric isomers, salts and salts of isomers,” appeared at 21
    C.F.R. § 1308.11(h).
    Section 1300.01(b) of Title 21 of the Code of Federal Regulations defines
    the term “isomer” and provides the sole regulatory definition for the term
    “positional isomer,” as used in Schedule I. See 21 C.F.R. § 1300.01(b). The DEA
    added the definition for “positional isomer” to § 1300.01(b) for the first time by
    final rule that became effective on January 2, 2008. See 72 Fed. Reg. 67,850,
    67851-52 (Dec. 3, 2007). Section 1300.01(b) defines “isomer,” in relevant part, as
    “(1) [t]he optical isomer, except as used in § 1308.11(d) . . . of this chapter. As
    4
    The original Schedule I may be found at 21 U.S.C. § 812. For purposes of the original
    Schedule I, 21 U.S.C. § 802(14) defines “isomer,” in relevant part, as “the optical isomer, except
    as used in [21 U.S.C. § 812,] schedule I(c) . . . . As used in [21 U.S.C. § 812,] schedule I(c), the
    term ‘isomer’ means any optical, positional, or geometric isomer.” The original Schedule I
    permanently lists certain hallucinogens at subsection (c), but to this day, § 812 does not define
    “positional isomer.” Section 812(c) specifically provides that the initial statutory schedules may
    be amended by the DEA through the process set forth in 21 U.S.C. § 811 and that they are
    published in the Code of Federal Regulations at 21 C.F.R. Part 1308. 21 U.S.C. § 812(c) n.1.
    5
    Case: 17-10397   Date Filed: 09/21/2018    Page: 6 of 30
    used in § 1308.11(d) of this chapter, the term ‘isomer’ means any optical,
    positional, or geometric isomer.” 
    Id. The definition
    of “isomer” then goes on in
    subsection (2) to define the term “positional isomer,” a definition we will discuss
    in a moment.
    But first, we note the DEA’s reasons for adding a definition of only
    “positional isomer” but not definitions for other types of isomers: “The terms
    ‘optical isomer’ and ‘geometric isomer’ are specifically defined and well
    understood scientific terms, and it is easy to determine whether one substance is an
    optical or geometric isomer of another.” 72 Fed. Reg. at 67,850. In contrast, the
    DEA acknowledged, “[t]he term ‘positional isomer” . . . is not universally defined,
    and, therefore, is subject to scientific interpretation.” 
    Id. For this
    reason, the DEA
    established its own definition of the term for purposes of the CSA. 
    Id. To better
    understand the issue in this case, we must delve into the science
    behind the DEA’s definition.       Isomers are “[m]olecules that share the same
    chemical formula but have their atoms connected differently, or arranged
    differently in space.”    Hydrocarbon structures and isomers, Khan Academy,
    https://www.khanacademy.org/science/biology/properties-of-carbon/hydrocarbon-
    structures-and-functional-groups/a/hydrocarbon-structures-and-isomers            (last
    visited Sept. 20, 2018).    The way that the atoms are arranged or connected
    determines the type of isomers the molecules form. See 
    id. 6 Case:
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    Two fundamental types of isomers exist: stereoisomers and constitutional
    isomers, which are also known as structural isomers. Isomers, Khan Academy,
    https://www.khanacademy.org/science/biology/properties-of-carbon/hydrocarbon-
    structures-and-functional-groups/v/isomers (last visited Sept. 20, 2018).                 Each
    isomer type, in turn, has sub-types. Optical and geometric isomers, which are
    mentioned in the DEA’s definition of “isomer,” are sub-types of stereoisomers.
    Positional isomers—also noted in the DEA’s definition of “isomer”—are a sub-
    type of constitutional isomers. We concern ourselves here with only positional
    isomers. 5
    5
    For those who must know more, the other sub-types of isomers mentioned in §
    1300.01—optical isomers and geometric isomers—are kinds of stereoisomers, meaning that they
    share the same bonding, in addition to sharing the same constituent atoms. Isomer, Khan
    Academy,       https://www.khanacademy.org/science/biology/properties-of-carbon/hydrocarbon-
    structures-and-functional-groups/v/isomers, at 3:55-4:21. Geometric isomers include cis-trans
    isomers. Unlike with structural isomers, the atoms of geometric isomers are connected in the
    same order, but the configuration of atoms around their bonds differs:
    Hydrocarbon structures and isomers, https://www.khanacademy.org/science/biology/properties-
    of-carbon/hydrocarbon-structures-and-functional-groups/a/hydrocarbon-structures-and-isomers
    (last visited Sept. 20, 2018) (citation omitted). As for optical isomers, they are also known as
    enantiomers. Optical isomers have the same chemical structure but their three-dimensional
    placement of atoms differs. Optical isomers are mirror images of one another and cannot be
    superimposed:
    7
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    Unlike in stereoisomers, the atoms in constitutional isomers differ in how
    they    are     connected.        See   Bond-line    Structures,     Khan    Academy,
    https://www.khanacademy.org/science/organic-chemistry/gen-chem-review/ bond-
    line-structures/v/structural-constitutional-isomers-new, at 2:45-2:59 (last visited
    Sept. 20, 2018). So although constitutional isomers share the same constituent
    atoms in the same numbers, those atoms are bonded together in different orders.
    See       Hydrocarbon         structures       and    isomers,     Khan      Academy,
    https://www.khanacademy.org/science/ biology/properties-of-carbon/hydrocarbon-
    structures-and-functional-groups/a/hydrocarbon-structures-and-isomers            (last
    visited Sept. 20, 2018).          The diagram below shows a basic example of a
    constitutional isomer:
    Hydrocarbon                       structures                 and              isomers,
    https://www.khanacademy.org/science/biology/properties-of-carbon/hydrocarbon-
    structures-and-functional-groups/a/hydrocarbon-structures-and-isomers            (last
    visited Sept. 20, 2018). As this illustration demonstrates, the four carbon atoms in
    See 
    id. (citation omitted).
                                                   8
    Case: 17-10397      Date Filed: 09/21/2018     Page: 9 of 30
    butane are connected to each other in a chain (so no carbon atom is bonded to more
    than two other carbon atoms), whereas one of the four carbon atoms in isobutane
    has three bonds to other carbon atoms. Similarly, while only two carbon atoms in
    butane are each bonded to three hydrogen atoms, in isobutane, three carbon atoms
    are each bonded to three hydrogen atoms, and one carbon atom is bonded to a
    single hydrogen atom. As a result, although both of these molecules share the
    same chemical formula (C4H10), they are different substances.
    As we have noted, a positional isomer is a type of constitutional isomer. In
    relevant part, the DEA has defined the term “positional isomer” in 21 C.F.R. §
    1300.01(b) to mean “any substance possessing the same molecular formula and
    core structure and having the same functional group(s) and/or substituent(s) as
    those found in the respective Schedule I hallucinogen, attached at any position(s)
    on the core structure . . . .” As the government and Phifer agree, butylone and
    ethylone are positional isomers of each other under this definition.
    For starters, butylone and ethylone both have the same molecular formula—
    C12H15NO3. Second, they share the same core structure—phenethylamine—as
    represented by the bold lines 6:
    6
    Not all carbon and hydrogen atoms are expressly identified in diagrams of more
    complex molecules such as ethylone or butylone. See Understanding Skeletal Formulae,
    Cambridge                                 Chemistry                                Challenge,
    http://www.c3l6.org/files/C3L6_Understanding_Skeletal_Formulae.pdf (last visited Sept. 20,
    2018). Rather, they are understood to be there, based on the bonding properties of carbon and
    hydrogen. See 
    id. 9 Case:
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    And third, butylone and ethylone have the same functional groups 7—amine,
    ketone, and ether—as indicated by the bold lines:
    II.
    With this information under our belts, we review the events that resulted in
    this appeal.
    Phifer was indicted for, on May 20, 2015, possessing with intent to
    distribute “a substance and mixture containing a detectable amount of a positional
    isomer of [b]utylone, also known as [e]thylone . . . .” He pled not guilty and went
    to trial.
    At trial, Phifer did not dispute that he possessed ethylone. Rather, his entire
    defense rested on the contention that, at the time of his arrest, ethylone was not a
    controlled substance under the CSA because it was not a “positional isomer” of
    7
    A functional group is a “specific grouping of elements that is characteristic of a class of
    compounds, and determines some properties and reactions of that class.” Functional Group
    Names,        Properties,       and       Reactions,      Lumen        Boundless         Chemistry,
    https://courses.lumenlearning.com/boundless-chemistry/chapter/functional-group-names-
    properties-and-reactions/ (last visited Sept. 20, 2018).
    10
    Case: 17-10397       Date Filed: 09/21/2018         Page: 11 of 30
    butylone as the term “positional isomer” is used in 21 C.F.R. § 1308.11(h).
    Specifically, Phifer contended that the DEA’s definition of “positional isomer” as
    set forth at 21 C.F.R. § 1300.01(b) does not govern the meaning of the term
    “positional isomer” in § 1308.11(h)—which identifies only temporarily scheduled
    substances—because, by its language, the DEA’s definition applies to only those
    substances     listed    at   §    1308.11(d)—which          are     permanently      scheduled
    hallucinogens. And since, in Phifer’s view, the DEA supplied no definition for the
    term “positional isomer” as it appears in § 1308.11(h) (temporarily scheduled
    drugs), Phifer argued at trial that the “literal definition” of “positional isomer”
    applied to that term. According to Phifer, the “literal definition” of the term is the
    “scientific . . . meaning that is known commonly in the science world, what is
    taught to the chemists.”          And, Phifer contended, under the common science
    definition of “positional isomer,” ethylone is not a positional isomer of butylone.
    To testify to this “literal definition,” Phifer presented as an expert witness
    Dr. Gregory Dudley, Ph.D. 8 During his testimony, Dr. Dudley relied as an exhibit
    on the textbook called Organic Chemistry, 9 the textbook used to teach organic
    chemistry at the university where Dr. Dudley was tenured, and according to Dr.
    Dudley, a commonly used textbook. A page of the textbook explained, “Among
    8
    At the time of trial, Dr. Dudley served as the Eberly Family Distinguished Professor and
    department chair at the Department of Chemistry at West Virginia University. The government
    stipulated that he was an expert in organic chemistry.
    9
    John McMurry, Organic Chemistry (Cengage Learning 9th ed. 2015).
    11
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    the kinds of constitutional isomers we’ve seen are skeletal, functional, and
    positional isomers.”
    Dr. Dudley testified that skeletal isomers are isomers with different carbon
    skeletons. As an example of skeletal isomers, Dr. Dudley showed the jury the
    illustration below:
    Def. Ex. 1 (taken from 
    McMurry, supra
    ). He further explained that functional
    isomers are isomers that have different functional groups. So, for example, though
    ethyl alcohol and dimethyl ether both have the same number of carbon, hydrogen,
    and oxygen atoms in their composition, those atoms are arranged into different
    functional groups, like so:
    
    Id. And finally,
    Dr. Dudley stated that positional isomers have the same carbon
    skeleton (unlike skeletal isomers) and the same functional groups (unlike
    functional isomers) but that the functional group is attached to the carbon skeleton
    at a different position (the “McMurry definition”). So, for example, the functional
    groups in the skeletal isomers isopropylamine and propylamine are attached like
    so:
    12
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    Id. Under the
    McMurry definition of “positional isomer,” then, butylone and
    ethylone are not positional isomers because they do not have the same carbon
    skeletons, as diagramed here:
    Rather, butylone and ethylone are skeletal isomers.
    Whether isomers are positional or skeletal under the McMurry and DEA
    definitions differs because the DEA definition of “positional isomer” does not
    require two different substances to have the same carbon skeleton; in essence, it
    allows at least some skeletal isomers (under the McMurry definition) to count as
    positional isomers.
    Armed with this testimony, Phifer urged the district court to define
    “positional isomer” in the jury instructions, using the McMurry definition: a
    positional isomer is a constitutional isomer that has the same carbon skeleton and
    the same functional group but differ[s] from another in the location of the
    functional groups or in the carbon chain.”      The district court denied Phifer’s
    13
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    request. Instead, it used the DEA definition of “positional isomer” in the jury
    instructions. For its part, the government proffered that it could call its expert
    witness back on rebuttal to testify that the DEA definition is consistent with
    another accepted scientific definition, but the district court declined to hear the
    rebuttal testimony in light of its decision to instruct the jury on the DEA definition.
    The jury returned a verdict of guilty.
    III.
    Now, for the law.
    A.
    This case requires us to determine the definition of “positional isomer” as
    used in 21 C.F.R. § 1308.11(h).10             We begin by considering the regulatory
    language. See Christensen v. Harris Cty., 
    529 U.S. 576
    , 588 (2000). For if it
    clearly and unambiguously answers the precise question at issue, that is the end of
    the matter. See 
    id. Here, the
    precise question we must resolve concerns whether the definition
    of “positional isomer” in 21 C.F.R. § 1300.01(b) encompasses the term “positional
    10
    Phifer wisely does not challenge the DEA’s authority to add substances to the
    controlled-drug schedules or the DEA’s addition of butylone and, among other isomers, its
    “positional isomers” to Schedule I. Nor does he take issue with the DEA’s authority to define by
    rule-making what it means by the term “positional isomer.” Congress distinctly delegated to the
    Executive its power to perform these functions, and the Supreme Court has previously upheld the
    DEA’s authority to engage in these types of activities. See Touby, 
    500 U.S. 160
    . Phifer
    similarly does not assert that the DEA did not follow the required procedures in promulgating the
    regulations at issue.
    14
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    isomer” as used at 21 C.F.R. § 1308.11(h). As we have noted, the sole definition
    for the term “positional isomer” specified in the DEA’s regulations is the
    following:
    As used in parts 1301 through 1308 . . . of this chapter, the following
    terms shall have the meanings specified:
    ...
    As used in § 1308.11(d) of this chapter, the term “positional isomer”
    means any substance possessing the same molecular formula and core
    structure and having the same functional group(s) and/or
    substituent(s) as those found in the respective Schedule I
    hallucinogen, attached at any position(s) on the core structure, but in
    such manner that no new chemical functionalities are created and no
    existing chemical functionalities are destroyed relative to the
    respective Schedule I hallucinogen. . . .
    21 C.F.R. § 1300.01(b).
    The government and Phifer each assert that this definition is unambiguous.
    But of course, they claim it unambiguously means opposite things:               the
    government says the definition clearly covers the term “positional isomer” as used
    in § 1308.11(h), while Phifer argues it unambiguously excludes that term as used
    in §1308.11(h).
    We conclude that neither is correct; the regulatory language is ambiguous
    with respect to the precise question we must answer.
    On the one hand, the regulation provides the only definition of “positional
    isomer” in the DEA’s CSA regulations, and the prefatory language of section (b),
    15
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    which applies to all definitions listed in that regulation, purports to render all
    definitions listed applicable to “part[] 1308,” of which § 1308.11(h) is certainly a
    part. This language suggests that the definition covers use of the term “positional
    isomer” as it appears in § 1308.11(h).
    But on the other hand, the precise definition of “positional isomer” appears,
    by its use of the phrase “[a]s used in § 1308.11(d),” to limit the definition of that
    specific term to uses of it in § 1308.11(d). And, of course, § 1308.11(h) is not a
    part of § 1308.11(d).
    Nevertheless, the definition does not say “as used only in § 1308.11(d).” So
    the prefatory phrase could be read as mere surplusage. But the more natural
    reading of the definition suggests that the definition does not apply to §
    1308.11(h).
    In short, the language of the regulation is fairly susceptible of being read to
    answer our precise question—whether the definition of “positional isomer” found
    in § 1300.01(b) governs the meaning of that term as used in § 1308.11(h)—both
    affirmatively and negatively. The regulation is therefore ambiguous on the exact
    issue we must resolve.
    B.
    So in the alternative, the government contends we should defer to the DEA’s
    interpretation of its own regulations to define the term “positional isomer” that
    16
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    appears in § 1308.11(h) as it is defined § 1300.01(b). In support of this position,
    the government relies on so-called Auer deference. See Auer v. Robbins, 
    519 U.S. 452
    , 461 (1997). Auer deference provides that when a regulation is ambiguous, we
    defer to the promulgating agency’s interpretation of that regulation, unless its
    construction is “plainly erroneous or inconsistent with the regulation.” 11 See 
    Auer, 519 U.S. at 461
    (citing Robertson v. Methow Valley Citizens Council, 
    490 U.S. 332
    , 359 (1989) (quoting Seminole 
    Rock, 325 U.S. at 414
    )) (internal quotation
    marks omitted). As long as the agency’s interpretation of its own regulation
    “reflect[s] the agency’s fair and considered judgment on the matter in question,”
    
    Auer, 519 U.S. at 462
    , Auer requires deference to it—even if the agency’s
    interpretation appears for the first time in a legal brief in the very litigation at issue.
    See 
    id. at 462-63;
    Chase Bank USA, N.A. v. McCoy, 
    562 U.S. 195
    , 208-09 (2011).
    Here, the DEA points for its interpretation of the term “positional isomer” to
    its website at the time of Phifer’s arrest. At that time, the DEA maintained a list
    entitled “Controlled Substances” on its public website.                   That list identified
    butylone as a Schedule I controlled substance. And under “OTHER NAMES” for
    butylone, the list stated, among others, “Positional Isomers: ethylone (bk-MDEA;
    MDEC) . . .).” See Controlled Substances, Drug Enforcement Agency,
    11
    Auer deference is also sometimes referred to as Seminole Rock deference, for the case
    that originally formulated the standard in 1945. See Bowles v. Seminole Rock & Sand Co., 
    325 U.S. 410
    , 413 (1945); see, e.g., Decker v. Nw. Envtl. Def. Ctr., 
    568 U.S. 597
    , 616-17 (Scalia, J.,
    concurring in part and dissenting in part).
    17
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    https://web.archive.org/web/20150415055617/https://www.deadiversion.usdoj.gov
    /schedules/orangebook/c_cs_alpha.pdf (last visited Sept. 20, 2018).
    We agree with the DEA that if Auer deference applies here, we must defer to
    the DEA’s interpretation of § 1300.01(b)’s definition of “positional isomer” to
    govern the meaning of that term in §1308.11(h). The DEA’s website clearly
    identifies ethylone as a “positional isomer” of butylone for purposes of Schedule I.
    For reasons we have already explained, that interpretation is not “plainly erroneous
    or inconsistent with the regulation[s].” See 
    Auer, 519 U.S. at 461
    . And we have
    no “reason to suspect that the [DEA’s] interpretation does not reflect the agency’s
    fair and considered judgment on the matter in question.” See Christopher v.
    SmithKline Beecham Corp., 
    567 U.S. 142
    , 155 (2012) (citations and internal
    quotation marks omitted).      Nor is the website’s interpretation of the term
    “positional isomer” to apply to drugs listed at §1308.11(h) inconsistent with a prior
    position the DEA has taken. See 
    id. And the
    fact that it predates this litigation
    demonstrates that it is not a “post hoc rationalization advanced by an agency
    seeking to defend past agency action against attack.” 
    Id. (citations and
    internal
    quotation marks omitted) (alteration not reflected).
    But this is a criminal case. And Phifer argues that Auer deference is not
    appropriate in a criminal prosecution.        As Phifer notes, by definition, Auer
    18
    Case: 17-10397    Date Filed: 09/21/2018   Page: 19 of 30
    deference applies only when a regulation is ambiguous. But when a criminal
    regulation is ambiguous, Phifer contends, the rule of lenity governs instead.
    The rule of lenity holds that a law must speak “in language that is clear and
    definite” if it is to render something a crime. United States v. Bass, 
    404 U.S. 336
    ,
    347 (1971) (citation and internal quotation marks omitted).         Two principles
    underlie this rule. First, “a fair warning should be given to the world in language
    that the common world will understand, of what the law intends to do if a certain
    line is passed. To make the warning fair, so fair as possible the line should be
    clear.” 
    Id. at 348
    (citation and internal quotation marks omitted). And second, the
    separation-of-powers doctrine requires legislatures, not courts, to define crimes.
    See 
    id. Under the
    rule of lenity, when a criminal law is ambiguous, we resolve
    doubts in favor of the defendant. 
    Id. The government
    responds that Auer deference essentially trumps the rule of
    lenity in criminal cases. In support of this position, the government relies on
    Ehlert v. United States, 
    402 U.S. 99
    (1971). Ehlert is a criminal case where the
    Supreme Court had to resolve the meaning of an ambiguous regulation to
    determine whether Ehlert’s criminal conviction could stand. See 
    id. at 104-05.
    Under one interpretation, Ehlert committed a crime, but under the other, he did not.
    See 
    id. The Supreme
    Court applied what has since become known as Auer
    deference to defer to the agency’s reasonable construction of its own regulation in
    19
    Case: 17-10397       Date Filed: 09/21/2018       Page: 20 of 30
    upholding Ehlert’s conviction. 
    Id. at 105
    (citing, among other cases, Seminole
    
    Rock, 325 U.S. at 413-14
    ).
    Significantly, though, in Ehlert, the Court considered only the discrete
    question of whether the defendant’s or the agency’s interpretation should apply.
    Neither party even raised the rule of lenity, let alone suggested it might overcome
    Auer deference. As a result, Ehlert did not preclude later courts from concluding
    that the rule of lenity renders Auer deference inapplicable in criminal cases. See
    Webster v. Fall, 
    266 U.S. 507
    , 511 (1925) (“Questions which merely lurk in the
    record, neither brought to the attention of the court nor ruled upon, are not to be
    considered as having been so decided as to constitute precedents.”).
    And four years later, our predecessor Court effectively reached that very
    conclusion.     In Diamond Roofing Co., Inc. v. Occupational Safety & Health
    Review Commission, 
    528 F.2d 645
    , 649 (5th Cir. 1976), the Court expressly held,
    “If a violation of a regulation subjects private parties to criminal or civil sanctions,
    a regulation cannot be construed to mean what an agency intended but did not
    adequately express.” Rather, the regulatory agency “has the responsibility to state
    with ascertainable certainty what is meant by the standards [it] has promulgated.” 12
    
    Id. 12 The
    former Fifth Circuit relied in part on M. Kraus & Brothers, Inc. v. United States,
    
    327 U.S. 614
    (1946), for its holding. Like Ehlert, Kraus is a criminal case. In it, the defendants
    were indicted for violating a price-control regulation. 
    Id. at 616.
    Because the regulation was
    20
    Case: 17-10397        Date Filed: 09/21/2018        Page: 21 of 30
    The former Fifth Circuit gave two reasons for its conclusion. First, the
    public is entitled to “fair warning” of prohibited conduct if it can be penalized for
    engaging in such behavior. 
    Id. And second,
    the law “must provide a reasonably
    clear standard of culpability to circumscribe the discretion of the enforcing
    authority and its agents”—in other words, to maintain separation of powers
    between the legislature (the executive serving as the legislature’s agent) and the
    executive (serving as the executive). 
    Id. If these
    reasons sound familiar, that’s because, as we have noted, they
    underlie the rule of lenity. So though the Court did not mention the rule of lenity
    by name, it effectively invoked the doctrine to defeat Auer deference whenever a
    defendant faces civil or criminal penalties. See United States v. Moss, 
    872 F.3d 304
    , 308, 314 (5th Cir. 2017) (reaffirming Diamond Roofing’s holding that Auer
    deference is precluded in criminal cases).
    We are bound by Diamond Roofing. See Bonner v. City of Prichard, 
    661 F.2d 1206
    (11th Cir. 1981) (en banc) (decisions of the Fifth Circuit issued before
    the close of business on September 30, 1981, are binding precedent in the Eleventh
    ambiguous on the precise question at issue, the administering agency urged the Supreme Court to
    defer to its consistently maintained interpretation of the regulation. 
    Id. at 623
    & n.6. The
    Supreme Court declined. It explained that it did “not believe that, under the strict rule of
    construction [applicable to statutory regulations that detail crimes], such an interpretation of [the
    regulation] [was] dictated by its plain language.” 
    Id. at 624.
    And “[n]ot even the [agency’s]
    interpretations of [its] own regulations can cure an omission or add certainty and definiteness to
    otherwise vague language.” 
    Id. at 622.
    Interestingly, Ehlert does not mention Kraus at all.
    21
    Case: 17-10397      Date Filed: 09/21/2018       Page: 22 of 30
    Circuit). For that reason, we hold that Auer deference does not apply in criminal
    cases, and instead, we must look solely to the language of the regulatory provision
    at issue to determine whether it unambiguously prohibits the act charged.
    C.
    When we consider the regulations at issue here, we cannot ascertain on this
    record whether, at the time of Phifer’s actions, the language of the regulations
    unambiguously prohibited possession with intent to distribute ethylone. We know
    that § 1300.01(b)’s definition of “positional isomer” does not govern the meaning
    of that term in § 1308.11(h).13 But we do not know what does.
    True, the meaning of “positional isomer” in § 1308.11(h) presents a question
    of law for the court to decide. See McDermott Int’l, Inc. v. Wilander, 
    498 U.S. 337
    , 356 (1991). But the court must ascertain the meaning of this technical term
    by looking to the science in which the term is used. See Corning Glass Works v.
    Brennan, 
    417 U.S. 188
    , 201 (1974).
    13
    Nothing precludes the DEA in the future from going through the rulemaking process to
    amend § 1300.01(b)’s definition of “positional isomer” to encompass all uses of that term in §
    1308.11, including those found at § 1308.11(h). Nor, if the DEA had not already amended its
    permanent Schedule I to add butylone and its positional isomers to § 1308.11(d), would anything
    have prevented it from engaging in the roughly 30-day process to temporarily add ethylone to
    Schedule I. The problem here, though, is that it did neither of those things as of the time of
    Phifer’s arrest. See Matter of Metro-East Mfg. Co., 
    655 F.2d 805
    , 811 (7th Cir. 1981) (“It would
    impose no hardship on the Secretary to amend the rules to give ‘fair warning’ of the types of
    investigation deemed ‘reasonable.’”).
    22
    Case: 17-10397        Date Filed: 09/21/2018       Page: 23 of 30
    And to do that, the district court must conduct an evidentiary hearing 14 and
    determine the definition or definitions of “positional isomer” that are generally
    accepted within the scientific community. 15 At this evidentiary hearing, essentially
    a modified Daubert hearing,16 the district court must assess the reliability of any
    evidence offered by the parties, considering to the extent they are reasonable
    measures of reliability in this context, the specific “reliability” factors mentioned
    in 
    Daubert, 509 U.S. at 593-94
    , as well as any other relevant factors, see Kumho
    Tire Co., Ltd. v. Carmichael, 
    526 U.S. 137
    , 141 (1999) (“the test of reliability is
    ‘flexible’” (quoting Daubert, 
    509 U.S. 579
    )).                    It must also consider the
    qualifications of any witness presenting evidence. After evaluating all evidence
    offered, the district court must determine by a preponderance of the evidence what
    definition or definitions of “positional isomer” are generally accepted within the
    scientific community. 17 See Allison v. McGhan Med. Corp., 
    184 F.3d 1300
    , 1306
    14
    If the parties are amenable, the district court can forego the evidentiary hearing and
    instead accept stipulations of definitions of “positional isomer” that the parties agree are
    generally accepted in the scientific community.
    15
    This does not violate Alleyne v. United States, 
    570 U.S. 99
    (2013). “Positional isomer”
    is merely a definition of a term in a regulation, and it is the duty of the courts to ascertain the
    definitions of words as they are used in the law. See 
    McDermott, 498 U.S. at 356
    . Plus, as we
    explain, the district court may not choose what it deems to be the best definition; instead, it
    simply fulfills a gatekeeping function in identifying all definitions of the term that are generally
    accepted within the scientific community.
    16
    Daubert v. Merrell Dow Pharms., Inc., 
    509 U.S. 579
    (1993), and its progeny set forth
    the district court’s responsibilities in conducting an evidentiary hearing concerning the
    admissibility of expert testimony under Rule 702, Fed. R. Evid.
    17
    Because the district court did not pass on whether the McMurry definition is generally
    accepted in the scientific community and the government did not have the opportunity to object
    to the McMurry definition under the framework set forth in this opinion, should Phifer wish to
    23
    Case: 17-10397      Date Filed: 09/21/2018       Page: 24 of 30
    (11th Cir. 1999) (identifying preponderance of the evidence as the standard of
    admissibility in a Daubert hearing).
    The court may not choose among multiple definitions that are generally
    accepted within the scientific community.              It must credit all definitions of
    “positional isomer” that the parties show to be generally accepted within the
    scientific community. Then, during the criminal trial, in the jury instructions, the
    district court must define “positional isomer” in all ways that it has found are
    generally accepted within the scientific community. It is for the jury to decide
    whether, as a matter of fact, ethylone satisfies all of the generally accepted
    definitions of a “positional isomer” of butylone, on which the district court
    instructs it. If the jury concludes that it does not meet at least one such definition,
    the rule of lenity requires it to return a verdict of not guilty. But if the jury finds
    that ethylone qualifies as a “positional isomer” of butylone under all definitions of
    that term that the district court provides to it, the jury should return a verdict of
    guilty.
    D.
    Finally, we reject Phifer’s claim that retrying him would violate double
    jeopardy. The Double Jeopardy Clause of the Fifth Amendment provides, “[N]or
    rest on the McMurry definition, he should either re-present the evidence or obtain the
    government’s stipulation that the McMurry definition is generally accepted within the scientific
    community.
    24
    Case: 17-10397     Date Filed: 09/21/2018   Page: 25 of 30
    shall any person be subject for the same offense to be twice put in jeopardy of life
    or limb.” U.S. Const. amend. V. But “[i]t has long been settled . . . that the
    Double Jeopardy Clause’s general prohibition against successive prosecutions does
    not prevent the government from retrying a defendant who succeeds in getting his
    first conviction set aside, through direct appeal . . . , because of some error in the
    proceedings leading to conviction.” Lockhart v. Nelson, 
    488 U.S. 33
    , 38 (1988);
    see also Delgado v. Fla. Dep’t of Corr., 
    659 F.3d 1311
    , 1324 (11th Cir. 2011)
    (citing and quoting Lockhart). Here, Phifer alleges no prosecutorial misconduct,
    and we can find no other reason why the Double Jeopardy Clause would preclude
    retrial.
    IV.
    For these reasons, we vacate Phifer’s conviction and remand for further
    proceedings consistent with this opinion.
    REVERSED AND REMANDED.
    25
    Case: 17-10397        Date Filed: 09/21/2018       Page: 26 of 30
    JORDAN, Circuit Judge, concurring:
    I concur in and join Judge Rosenbaum’s opinion for the court. Although the
    task for the district court on remand is an unusual one, I cannot think of a better
    alternative given the circumstances. Cf. United States v. Kelly, 
    2016 WL 8732182
    ,
    *5 (D. Nev. 2016) (“The question of whether ethylone is an isomer of butylone—
    specifically, a positional isomer—is a question for the jury.”), aff’d, 
    874 F.3d 1037
    (9th Cir. 2017).1
    As the court correctly explains, the DEA has failed to define the term
    “positional isomer” for the temporary listings in 21 C.F.R. § 1308.11(h). The only
    regulatory     definition     of   “positional       isomer”    is   found     in    21    C.F.R.
    1300.01(b)(21)(ii), but that definition, given its qualifying language—“[a]s used in
    § 1308.11(d) of this chapter”—does not include § 1308.11(h). See Burgess v.
    United States, 
    553 U.S. 124
    , 130 (2008) (“As a rule [a] definition which declares
    what a term ‘means’ . . . excludes any meaning that is not stated.”) (citation and
    internal quotation marks omitted). In my view, this definitional void may present a
    1
    Kelly is the only reported case which involves a criminal charge based on ethylone being a
    positional isomer of butylone. But Kelly is of little help here because the defendant in that case,
    who pled guilty, did not contest that ethylone is a positional isomer of butylone. See 
    Kelly, 874 F.3d at 1045
    .
    26
    Case: 17-10397        Date Filed: 09/21/2018       Page: 27 of 30
    vagueness problem even if, as the district court concluded, it was the result of “an
    unintentional drafting omission.” D.E. 65 at 3.2
    When a term is not defined in a statute, the general rule is that “legislative
    purpose is expressed by the ordinary meaning of the words used.” Russello v.
    United States, 
    464 U.S. 16
    , 21 (1983). And when the undefined term is a term of
    art, the presumption is that “Congress intended it to have its established meaning.”
    McDermott Int’l, Inc. v. Wilander, 
    498 U.S. 337
    , 342 (1991). So far so good. But
    when the undefined term of art does not have a settled meaning, we cannot use the
    McDermott presumption, as the Supreme Court told us in De Pierre v. United
    States, 
    564 U.S. 70
    , 79 n.8 (2001) (explaining that McDermott does not apply
    “when there is no ‘settled meaning’—scientific or otherwise”).
    An “isomer” is a “compound[ ] with the same chemical formula [as another
    substance] but different structures.”          D.E. 98 at 50.        See also The American
    Heritage Dictionary of the English Language 928 (4th ed. 2009) (defining isomer
    as “[a]ny two or more substances that are composed of the same elements in the
    same proportions but differ in their properties because of differences in the
    arrangement of atoms”). On this record, there are at least two possible (and
    2
    I am not persuaded by the government’s argument that the DEA intended the definition of
    “positional isomer” in § 1300.21(b)(21)(ii) to apply to the temporary listings in § 1308.11(h).
    See Br. for the United States at 20-23. Even assuming that such an intent was likely,
    “[p]robability is not a guide which a court, in construing a penal statute, can safely take.” United
    States v. Wiltberger, 
    18 U.S. 76
    , 105 (1820). The DEA can, of course, fix the problem by
    enacting a regulation that defines “positional isomer” for purposes of § 1308.11(h).
    27
    Case: 17-10397     Date Filed: 09/21/2018    Page: 28 of 30
    scientifically accepted) definitions of the term “positional isomer.” One is the
    government’s definition, as set forth in § 1300.01(b)(21)(ii), and the other is the
    one provided by Mr. Phifer’s expert. The difference between these two definitions
    concerns the carbon skeleton of the isomer. The government’s definition does not
    require an identical carbon skeleton for an isomer to be “positional,” while Mr.
    Phifer’s definition does. These two definitions, however, do not necessarily
    constitute the relevant universe. As the court explains in its remand instructions,
    the district court must instruct the jury on all definitions of “positional isomer” that
    it finds are generally accepted in the scientific community.
    Conceivably, the jury here could be given a handful of definitions for the
    term “positional isomer.”     In my own non-exhaustive research, I have found
    several definitions in the case law and literature, though I cannot confidently say
    that they are generally accepted, or that the differences in wording are significant
    in a legal or scientific way. See Procter & Gamble Co. v. Teva Pharmaceuticals
    USA, Inc., 
    566 F.3d 989
    , 995 (Fed. Cir. 2009) (describing positional isomers as
    “contain[ing] the same atoms arranged in different ways”);                  2 Concise
    Encyclopedia of Science & Technology 1514 (McGraw-Hill 6th ed. 2009)
    (“Positional isomers . . . have the same functional group but differ in its position
    along a chain or in a ring.”); Dorland’s Illustrated Medical Dictionary 965 (32nd
    ed. 2012) (defining “positional isomerism” as “a type of constitutional isomerism
    28
    Case: 17-10397    Date Filed: 09/21/2018   Page: 29 of 30
    in which the position occupied by a carbon or atom differs with reference to the
    same fundamental carbon chain”).
    Criminal statutes and regulations need to be written in a way that allows a
    reasonable person to understand what is prohibited. This is not only an expectation
    of good government, it is a demand of constitutional proportions.          See, e.g.,
    Maynard v. Cartwright, 
    486 U.S. 356
    , 361 (1988); United States v. Edgar, 
    304 F.3d 1320
    , 1327 (11th Cir. 2002).
    If there are a handful of generally accepted definitions of “positional isomer”
    in the scientific community, there might be an as-applied vagueness problem. In
    that scenario it would be difficult to see how a reasonable person could have
    known in 2015 whether ethylone was a “positional isomer” of butylone. That
    reasonable person would have had to survey the scientific community, figure out
    which definitions of “positional isomer” were generally accepted, and then try to
    apply each of those definitions to ethylone. Cf. United States v. Apex Oil Co., Inc.,
    
    132 F.3d 1287
    , 1291 (9th Cir. 1997) (dismissing criminal charge because the word
    “petroleum” was not defined in the applicable regulation: “In the face of
    uncertainty as to the meaning of what is forbidden, the rule of lenity requires
    dismissal of count one of the indictment.”). On the other hand, the government
    points out that, notwithstanding any general vagueness concerns, there is evidence
    that here Mr. Phifer knew he was engaging in illegal conduct (e.g., by admitting to
    29
    Case: 17-10397    Date Filed: 09/21/2018   Page: 30 of 30
    law enforcement that the way the ethylone was packaged and imported led him to
    believe it was illegal). And that, says the government, eliminates any vagueness
    claim. See Br. for the United States at 27 (citing United States v. Carlson, 
    87 F.3d 440
    , 444 (11th Cir. 1996)). Given that we are remanding for an evidentiary
    hearing, I do not express any view how any vagueness issue should be resolved.
    30