SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS Acyclics, Monocyclics, Bicyclics A report of the Nomenclature Committee of the Division of Organic Chemistry, American Chemical Society Number fourteen of the Advances in Chemistry Series Edited by the staff of Industrial and Engineering Chemistry Published March 1955 by AMERICAN CHEMICAL SOCIETY 1155 Sixteenth Street N.W. Washington 6, D. C. In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.fw001 Copyr ight 1955 by A M E R I C A N C H E M I C A L SOCIETY All Rights Reserved In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.fw001 FOREWORD Wide agreement as to a clear and useful nomenclature is of great benefit in any field of science. The nomenclature here presented merits wide acceptance among terpene and other interested chemists because of the thorough way in which the careful work was done. Many versed in the chemistry of terpenes and many others experienced in naming chemical compounds were consulted. Full opportunity for criticism was offered. The proposed system of nomenclature for terpene hydro- -carbons has been accepted by the Nomenclature Committee of the American Chemical Society's Division of Organic Chemistry (Committee A) and approved by the American Chemical Society (ACS) on recommendation of its general Nomenclature, Spelling, and Pronunciation Committee. Furthermore the Commission on the Nomenclature of Organic Compounds of the International Union of Pure and Applied Chemistry (IUPAC) has agreed to accept these nomenclature recommendations and has expressed intention to recommend them for acceptance by IUPAC on the custom- -ary tentative basis. In working up the rules much information was brought together which should be of real help in the reading of terpene literature. Accordingly, the essential portion of this information is given in this monograph in addition to the officially approved nomenclature rules, examples, and discussion. The index by common terpene names will guide readers to structural formulas and recommended names. The traditional nomenclature used in the terpene field is at best an exacting exercise in memory. Most of the terpene names are derived from the genus or family names of plants or from the essential oils from which the products were first isolated or in which they occur most abundantly. Many terpene names used in the past, both for fundamental structures and for derivatives, especially the latter, give no clue as to the nature of the specific compounds or as to the struc- -tural relationships which exist among several terpenes or between terpenes and similar organic compounds. The close chemical and biogenetical interrelationships of the terpenes justify treatment as a special field, and the necessity for introducing some systematization into the nomenclature had become more and more evident as knowledge of the field continued to expand. Terpenes can be named systematically by the general nomenclature rules of IUPAC and recognized extensions of those rules, but the resulting names are fre- -quently unmanageably long and complicated, are difficult in speech, and conceal the terpene nature of the compounds. Therefore, in 1946 Committee A (then led by Howard S. Nutting, later by Mary Alexander) set up a Subcommittee on Nomenclature of Terpenes under the chairmanship of Mildred W. Grafflin to explore the possi- -bility of developing an alternative, consistent, unambiguous, and workable scheme for naming terpenes. The chairman of this subcommittee was its sole official mem- -ber; she did an enormous amount of careful work. Leonard T. Capell, Charles D. Hurd, Howard S. Nutting, Austin M. Patterson, and Louis Schmerling, all members of Committee A, served as consultants continuously during the development of this project to its present stage. In addition, more than 50 terpene chemists, organic chemists, and nomenclaturists, both American and European, criticized various drafts of proposals and offered constructive suggestions and stimulating ideas that i i i In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.fw001 aided immeasurably in resolving controversial points, revising initial proposals, and directing necessary decisions. They all now have indicated their approval of the final recommendations here reported. The official ACS report is limited to the naming of the simple acyclic, mono­ -cyclic, and bicyclic terpene hydrocarbons because official action has been taken only on the recommendations relating to these three classes of terpenes. The term "terpene hydrocarbons" is intended to include not only the numerous C10H16 hydrocarbons but also their hydrogenated derivatives and other hydrocarbons possessing similar fundamental structures; they may be of natural or synthetic origin. During the developing work which has led to the mature report here given, there have been three long typescript versions of the terpene nomenclature report (April, 1949, June, 1950, and June, 1952, respectively) and one condensed type­ -script version (September, 1953). In addition the work was presented briefly by Miss Graff lin under the title "Nomenclature of Terpene Hydrocarbons and Related Compounds" at a Symposium on Nomenclature of Hydrocarbons held in 1949 by the ACS Division of Petroleum Chemistry and preprinted along with the other papers of this symposium. Furthermore, Austin M. Patterson presented a preview of this nomenclature in his column in Chemical and Engineering News (Cbem. Eng. News 30, 930-5(1952)). It should be noted that the present report differs in some respects from the proposals in these earlier, more or less widely circulated versions. The nomenclature rules, as recommended by a joint meeting of the National Research Council Subcommittee on Organic Nomenclature and Committee A at Buffalo, Ν. Y . , March 23, 1952, have been revised slightly in this published ver­ -sion in order to limit " n o r " to its traditional meaning in the terpene field, that is, to denote a ring system devoid of methyl groups. The parent saturated ring struc­ -ture of t ha jane is designated by the name bicycloB.l.OThexane instead of by northujane. This action was taken by Committee A at its meeting in Chicago, Illinois, September 5, 1953. For a task well done with exceptional thoroughness Miss Mildred W. Grafflin deserves the gratitude of all chemists who will have an opportunity to benefit by this full nomenclature report. She has mine. E. J. Crane, Chairman Committee on Nomenclature, Spelling, and Pronunciation American Chemical Society In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.fw001 Nomenclature Rules for Terpene Hydrocarbons Approved by the Council, American Chemical Societyª The general principles underlying the Fundamental terpene types: recommended scheme for systematizing the nomenclature of acyclic, monocyclic, and 7 C H , bicyclic terpene hydrocarbons are: 1. Application of IUPAC and recognized rules to the naming and numbering of the a (Tcycpleic B a)n dm othneo cdyicmliect hcyolmcypcoluonhdexsa. nIen- teyapceh H 2 C » « O H , 1 0 C H 3 of these classes of hydrocarbons there exists no outstanding common terpene name or Λ structure to serve as the basis for develop­ / C H \ ing a logical series of simple terpene-like H,C * CH, names. t 10 H2è» / «CH, 2. Reduction of the chemical structures of the remaining simple monocyclic and Menthane bicyclic hydrocarbons to five fundamental (p-form) types. H,C 7 C H , 3. Asignment of fixed numberings to s 9 ltahreg feirv eth taynp itchael rcianrgb-ocnar sbkoenle tsoknesle twonhsi.c h are 10CH3 II 4. Well known terpene names are re­ Thujane tained for the parent compounds of four Λ of these fundamental types and a new ter­ pene-like name, bornane, is recommended H , C Ryh . *lmt for the fifth, to replace camphane and bornylane. 10CH1 5. The nor- type of name (nor- in the H,Ct traditional terpene sense of complete strip­ ping of methyl groups from the ring) is III used for ring-carbon skeletons where con­ Carane venient. 6. Development» on the basis of the H » C / \ y names of the larger parent compounds » H easntda btlhiseh nedo r-n sotmruecntculraetsu raen dr uwleitsh, othf el oagidic oafl PiInVan e series of simple names which are suffi­ ciently definitive to show immediately the H,C« Î C H , relations among compounds of a single |H,C—C—CH,| series and which are exceedingly useful in H,C, 8 ρ · ,CH, the spoken language. 7. The following structures, numberings, H and names are used: V * March 27, 1954, 125th national meeting. Bornane Kansas City, Mo. In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.pr001 A D V A N C E S I N C H E M I S T R Y S E R I E S Nor- structures: naming each class of the simple terpene hydrocarbons are: H , Η, Acyclics: H 2 C 2 4CHj The acyclic terpene hydrocarbons will Α . be named in a manner similar to other C H . I unsaturated aliphatic hydrocarbons H C l «4CHi2 (IUPAC rules) when pure compounds are H 2 c / ^ c / ^ Η involved. Example: 7-methyl-3-methylene- H2C» 1,6-octadiene. H VI Monocyclics: Norearane VII Norpinane Menthane Type: For this type of mono­ H cyclic terpene hydrocarbon (para, ortho, and meta isomers of menthane) the men­ thane, menthene, and menthadiene names H2C§ 2 C H 2 and the well-established fixed numbering CH ι * I of menthane (Formula I above) will be H2C» I7 »CH, used. Examples: T C H , 7CH3 VIII I Norbornane / Ν /?\ The nomenclature system outlined in this H2Ce 2CH report folows many customary terpene H2Ç* 2CH2 C H j 1 1 p nroamcteinccelsa tbuuret arulsloe sc aonfdo rpmras ctioc eess. taTbhliesh red­ ΗΛN e / aCH—CH\.7 C9 H3 H2Cg 3CH2 sulting terpene-like names are much sim­ H 2 10 pler than the strict systematic names m-Menthane / C H \ formed acording to IUPAC rules. Re­ 9 10 placement of the currently used common , C H 3 1-p-MentheiH» terpene names by the recommended ter­ pene-like pseudosystematic names will facilitate ready recognition of the terpene H ,. C ,. JaC H hydrocarbon structures and will aid in integrating terpene chemistry with the en­ H2C5 3^Η« tire field of organic chemistry. Extension of the hydrocarbon rules to the naming of functional derivatives will simplify and unify nomenclature within the terpene H a C / ^ C H s 9 10 field. 1,4(8)-#-Menthadiene Stereoisomers and Their Nomenclature Stereoisomers among the terpenes are Dimethylcyclohexane Type: This type abundant and exceedingly important to the of monocyclic terpene hydrocarbon will be chemistry of the field. Stereochemical no­ named systematically as derivatives of menclature therefore cannot be ignored in cyclohexane, cyclohexene, and cyclohexa- any complete scheme for systematizing diene (IUPAC rules). terpene nomenclature. The recommenda­ Examples: tions in this report provide only structural names for the acyclic, monocyclic, and H,C CH3 bicyclic terpene hydrocarbons. Studies in various fields (e.g., steroids) on preferred X methods of designating isomeric configura­ tions are being made. H2Ce 2CH—CH3 Recommendations The specific recommendations made by the American nomenclature committees for H, In SYSTEM OF NOMENCLATURE FOR TERPENE1 ,H1,Y2,D3-RTOetCrAamRBetOhNylS-; Advances in Chemistry; American Chemical Society: Washciyncgltoohne, xDaCn,e 1 955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.pr001 N O M E N C L A T U R E F O R T E R P E N E H Y D R O C A R B O N S identical with that of carane but contain C H 3 substituents such that the principle of like treatment of like things will be violated by using the carane, carene, and caradi- H.Cf 2 C — C H 3 ene names, the nor- type of terpene names H ! based on systematic bicyclo numbering H C C / ° \ £ / X J H , will be used (see Formula VI). Ex­ amples: 2,4-norcaradiene, 3,4,7,7-tetra- H , methylnorearane. 1,2,3,3-Tetramethyl- ÇH, Ρ inane Croup ( Bicyclo [3.1.1 ] heptane cyclohexene I Type): The pinane-type bicyclic terpene hydrocarbons will be named as pinanes, H , C e 2 C H pinenes, and pinadienes, and these names H 3 C X I I will be based on the recommended fixed >C 5 , C H numberings of the pinane carbon skeleton H 3 C / \ £ / (see Formula IV). For those derivatives Η which contain ( 1 ) fewer carbon atoms than pinane, (2) the same number as, or more 1,5,5-Trimethyl- carbon atoms than, pinane but do not have 1,3-cyclohexadiene a carbon skeleton identical with that of pinane, or (3) more carbon atoms than Bicyclics: pinane and a carbon skeleton identical with that of pinane but contain substituents Thujane Croup (Bicyclo[3.1.0]hexane such that the principle of like treatment Type): The thujane-type bicyclic ter­ of like things will be violated by using the pene hydrocarbons will be named as thu- pinane, pinene, and pinadiene names, the janes, thujenes, and thujadienes, and these nor- type of terpene names based on names will be based on the recommended systematic bicyclo numbering will be used fixed numbering of the thujane carbon (see Formula VII). Examples: 2(10),3- skeleton (see Formula II). For those de­ pinadiene, 4-methylenepinane, 6,6-di- rivatives which contain (1) fewer carbon methyl-2-vinyl-2-norpinene. atoms than thujane, (2) the same number as, or more carbon atoms than, thujane but Bornane Croup ( Bicyclo [2.2.1 ] hep­ tane Type): The new name bornane is do not have a carbon skeleton identical recommended to replace "camphane." The with that of thujane, or (3) more carbon bornane-type bicyclic terpene hydrocarbons atoms than thujane and a carbon skeleton will be named as bornanes, bornenes, and identical with that of thujane but contain bornadienes, and these names will be based substituents such that the principle of like on the recommended fixed numbering of treatment of like things will be violated by the bornane carbon skeleton (Formula V using the thujane, thujene, and thujadiene above). For those derivatives which con­ names, the bicyclo [3.1.0]hexane-type tain ( 1 ) fewer carbon atoms than bornane, names based on systematic bicyclo num­ (2) the same number as, or more carbon bering will be used. Examples: 4(10)- atoms than, bornane but do not have a thujene, 5-isopropylbicyclo[3.1.0]hex-2- carbon skeleton identical with that of ene. bornane or (3) more carbon atoms than Carane Croup ( Bicyclo [4.1.0] hep­ bornane and a carbon skeleton identical tane Type): The carane-type bicyclic ter­ with that of bornane but contain substitu­ pene hydrocarbons will be named as car- ents such that the principle of like treat­ anes, carenes, and caradienes, and these ment of like things will be violated by us­ names will be based on the recommended ing the bornane, bornene, and boraadiene fixed numbering of the carane carbon names, the nor- type of terpene names skeleton (see Formula III). For those based on systematic bicyclo numbering derivatives which contain (1) fewer car­ will be used (see Formula VIII). bon atoms than carane, ( 2 ) the same num­ Camphene will be preferred to 2,2-di- ber as, or more carbon atoms than, carane methyl-3-methylenenorbornane for the un- but do not have a carbon skeleton identical substituted compound. Examples: 7,7- with that of carane, or (3) more carbon dimethylnorbornane, 2,7,7-trimethyl-2- atoms than carane and a carbon skeleton norbornene. In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.pr001 System of Nomenclature For Terpene Hydrocarbons Acyclics, Monocyclics, Bicyclics Prepared by Mildred W. Grafflin, chairman (1946-53) of Subcommittee on Nomenclature of Terpenes of the Nomenclature Committee of the Division of Organic Chemistry, American Chemical Society Introduction The necessity for introducing some systematization into the nomenclature of terpenes has become more and more evident as knowledge of the field continues to expand. The close chemical and biogenetical interrelationships of terpenes justify treatment as a special field. In any proposed systematic scheme of naming series of related compounds and their derivatives, the nomenclature of hydrocarbons is the logical starting point. The report presented herewith is limited to the naming of the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons because of- ficial ACS action has been taken only on the recommendations relating to these three classes of terpenes. The general sources used for information on terpenes and their nomenclature are listed (5, 6, 23, 30, 31, 40, 41, 45, 47, 51) in "Literature Cited. " Historical and Current Nomenclature The traditional nomenclature used in the terpene field is at best an exacting exercise in memory. Most of the terpene names are derived from the genus or family names of the plants or from the essential oils from which the products were first isolated or in which they occur most abundantly. Many terpene names cur- -rently used, both for fundamental structures and especially for derivatives, give no clue as to the nature of the specific compounds or to the structural relationships which exist among several terpenes or between terpenes and similar organic com- pounds. The earlier investigators considered their products homogeneous; later, a number of these were found to be mixtures not merely of isomers but in some cases mixtures of entirely different structures. Some of these compounds were then dis- tinguished from each other by prefixing Greek letters to established terpene names — e.g-t ce-, /S-, and y-terpene and α», /S-, and ô-pinene. Prefixes such as alio-, apo-, epi-, homo-, is o-, ne ο-, and nor-, or combinations of these as isoallo- and neoiso-, were also attached to the common terpene names to indicate real or assumed rela­ tionships of a new product to one already known — e.g., ocimene, allo-ocimene: terpinolene, isoterpinolene; camphane, isocamphane, apocamphane, and norcamphane; fenchene, isofenchene, isoallofenchene, and apoisofenchene. Other prefixes such as fencho- and pino- were introduced — e.g., fenchocamphorane and pinocamphane. 1 In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.ch001 2 A D V A N C E S IN C H E M I S T R Y S E R I E S When later investigations proved that some of the relationships originally assumed were incorrect, usage of many of these names persisted. The practice of (a) naming hydrogenated derivatives as hydro compounds of more unsaturated structures — e.g., dihydrodipentene and hydrodicamphene — and (b) assigning similar names such as terpinene, terpinolene, and terpin to compounds, either closely related as the first two are or widely different as the last compound is from the other two, has added to the confusion in the existing nomenclature of terpenes and related compounds. Simple names such as camphane and camphene do not apply, respectively, to a saturated and unsaturated single basic structure as the modern chemist would assume. The unsaturated structure corresponding to camphane has been called bornylene consistently, whereas the saturated structure correspond- ing to camphene has been called isocamphane or dihydrocamphene. As would be expected from the historical development of terpene nomenclature, products of the same composition but isolated from different sources by different investigators were, in some cases, given different names — e.g., ^-limonene has also been called hesperidene, citrene, carvene, cinene, di-isoprene, isoterebenthene, and cautchene. A specific form of one compound was frequently designated by a new name rather than by adding recognized prefixes to an established name — e.g., the dl- form of limonene was named dipentene. Later, when some products were found to differ only in name and not in structure, unanimity of opinion as to which name should be retained was often difficult to attain and hence several of the synonym names have been used interchangeably — e.g., thujane and sabinane, jS-pinene and nopinene. This lack of decision on a preferred name is reflected in the traditional names of a series of related derivatives — e.g., camphane rather than bornylane has been used almost invariably for the saturated structure but many of the derivative names con- tain the root born- rather than camph-. Many similar terpenes contain identical sub- stituents and differ only in the positions of double bonds, which may be in the ring, outside the ring, or both; others differ only in the number or type of substituents. These similarities are not evident from the common terpene names which are often even misleading. Sufficient information has been given to indicate the desirability and necessity for attempting to introduce some systématisation into terpene nomenclature sô that structural relationships and differences among terpenes can be readily recognized from the names of the compounds. A complete and satisfactory systematic nomen- clature for terpenes already exists — they can be named according to the general nomenclature rules of the International Union of Pure and Applied Chemistry (IUPAC) and recognized extensions of these rules. For example, by recognized rules and Chemical Abstracts alphabetical order of prefixes, a-terpinene can be named system- atically as l-isopropyl-4-methyl-l,3-cyclohexadiene; β-fenchene as 2,2-dimethyl- 5-methylenebicycloQ2.2.Qheptane. However, these systematic names are unman­ ageably long and complicated, are difficult to speak, and conceal the terpene nature of the compounds. This approach to systematization is neither practical nor desirable, and is definitely contrary to the spirit of Rule 1 of the Definitive Report (41) which states: " A s few changes as possible will be made in terminology universally adopted." The recommendations in this report offer an alternative scheme for naming terpenes. The resulting names are more concise and conform more closely to current terpene literature. The underlying principles of this scheme, which in this report are applied only to the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons but can be applied generally to the entire terpene field, will be summarized later. In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.ch001 N O M E N C L A T U R E F O R T E R P E N E H Y D R O C A R B O N S 3 Classification of Terpenes The term terpenes originally was applied to cyclic hydrocarbon structures with the empirical formula C J Q H J ^ or to their derivatives which occur in the essential oils of plants. These compounds have often been referred to as the " true" or "proper" terpenes. As knowledge of the chemistry of the terpene field developed, compounds related both chemically and biogenetically to the C J Q H J ^ hydrocarbons have been identified. Some natural products have been synthesized; other synthetic compounds resemble known terpene structures. Consequently, today the term ter­ penes is broader in scope than its original meaning. The term terpene hydrocarbons, to which this report is limited, includes not only the numerous C 1 0 H|£ hydrocarbons but also their hydrogenated derivatives and other hydrocarbons possessing similar fundamental chemical structures. They may be acyclic or cyclic, simple or com­ plex, and of natural or synthetic origin. Many of their carbon skeletons have been shown to consist of multiples of the isoprene nucleus, C 5 H g , which led Wallach (56) to suggest the name hemiterpene for isoprene. The cyclic terpene hydro­ carbons may be further classified as monocyclic, bicyclic, or tricyclic. The few known structures of the sesquiterpenes, C ^ F ^ and of the polyterpenes, (CjHg)^, indicate that these hydrocarbons may eventually be classified similarly to the simpler terpenes. Formulas for typical examples of these general classes of ter­ pene hydrocarbons are shown in Chart 1. Add to the above hydrocarbons their oxygenated and hydrogenated derivatives as well as other types of derivatives; include the interconversion, rearrangement, and degradation products of these hydro* carbons and their many derivatives; do not ignore the synthetic terpenes for which no natural counterparts have as yet been found; recognize the existence of stereo­ isomers among which, in general, no one form predominates — that is modern ter­ pene chemistry. Stereoisomers and Their Nomenclature Stereoisomers among the terpenes are abundant and exceedingly important to the chemistry of the field. Stereochemical nomenclature therefore cannot be ignored in any complete scheme for systematizing terpene nomenclature; for the present, however, the recommendations in this report provide only structural names for the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons. Studies in various fields — e.g., steroids — on preferred methods of designating isomeric configura­ tions are being made by other committees (1, 21, 25). The scope of this problem can be indicated by a brief consideration of the stereochemical nomenclature of hydroxy derivatives of the bicyclic terpenes. For the parent bicyclic hydrocarbon compound known in the literature at present as cam­ phane, the name "bornane" is recommended in this report. (Reasons for choosing "bornane" are discussed later under "The Bornane Hydrocarbons".) A mono- hydroxy derivative of bornane, on the basis of IUPAC rules (41 ), would be named as a bornanol. Two such derivatives have the common terpene names, borneol and isoborneol; these names, on the basis of recommendations in this report would both become 2-bornanol. Obviously, this is inadequate and additional designations are necessary to distinguish between the two stereoisomers. In the steroid field, a similar problem has been solved successfully (19, 26, 29) by using the Greek letters a and β, immediately after (with no comma interven­ ing) the position number of the substituted carbon atom, to indicate a configuration which is either trans or cis to a standard reference point in the molecular structure. In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955. Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.ch001