The IUPAC Rules for Naming Organic Molecules

1 In the Vol. 83 No. 11 November 2006 Journal of Chemical Education1633 Textbooks used for teaching undergraduate courses pro-vide basic Rules and examples for Naming monofunctionalcompounds. However, students of more advanced organicchemistry courses and graduate students dealing with morecomplex Molecules need a set of additional Rules and guide-lines to identify polyfunctional compounds. The followingsummary of general principles may also be useful to instruc-tors. The formation of the systematic name for an organiccompound involves several steps, to be taken as far as theyare applicable in the following order (1 5).

2 Step 1 Determine the principal functional group in the com-pound. When a compound contains more than one groupin Table 1, the principal group is that which has the highestprecedence. This principal group will be cited as a suffix; allother groups are cited as 2 Determine the parent hydrocarbon (principal chain orparent ring system):(a) If the principal group occurs in a chain, the principalchain is selected as(i) the chain containing the functional group of thehighest seniority as the parent.(ii) If more than one such a choice is possible, selectthe chain with the maximum number of multiplebonds.

3 (iii) If (i) and (ii) together are not definitive, thenchoose the chain with maximum length.(iv) If two chains of the same length are possible, choosethe one with maximum number of (butan-1-yl)-4-methylhexanalOHThe parent chain here contains six carbon IUPAC Rules for Naming Organic MoleculesWStanislaw SkoniecznyDepartment of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada; Nbelirtin----C- Nelirtinobrac--onaycOH)C(-bla--oxoOHC-ed yhedlabrac--lymrof)C(> Oeno--oxoHO-lo-c-yxordyhHS-loiht--lynafl usdHN-2)enima-(enaza-d)-onima(-lynazaeHN >)enimi-(enaza-d)-onimi(-enedilynazaeC> <Cene-*C- -Ceny-**RO-,R-,X-**-yxokla,-lykla,-olahO N-,rA-2,**-ortin,-lyraN-,ON-3,**-odiza,- osortin N2RS-,**(,-ozaidRlynaflus-) )C(tonseodti(edirdyhtnerapehtfoemanehtni dedulcnimotanobrac.)

4 ,slonehplanoitisopriehtdna,lorhtnanehp-1 ,lorhtna-1,lohthpan-1,lonehpllitseradica circipdna,lomyht,losercsahcus, , , ,'-otpacrem'otderreferpsi'-lynaflus'etub ,enimidnaenima-otevitanretlanasaenaza-sd nemmocerCAPUI ecnerefer,seugolatac, )-onima(enima-esullitserutaretilcifitnei csdna,skoob, *.elbatpeccaerahcihw,)-onimi(sixiffuseht ,elucelomehtnitneserpsipuorgytiroirprehg ihafiytiroirprehgihehtfoxiffusehtybdewol lofsitidna-ne-otdegnahcpuorgytiroirprehg ihafi, **.puorgdewollofsitidna-ny-otdegnahcsixi ffuseht, **.puorgytiroirprehgihehtfoxiffusehtybIn the Classroom1634 Journal of Chemical Education Vol.

5 83 No. 11 November 2006 (b) If the principal functional group occurs in a cyclic sys-tem, that system forms the (octan-1-yl)cyclohexanolOHStep 3 Name the parent structure and the principal group(s).Give the parent the same name as if it were an alkane, butreplace -ane with the suffix characteristic of the functionalgroup of the highest priority (Table 1). Note: Multiple un-saturation in hydrocarbons is indicated by the numerical pre-fixes di-, tri-, etc. In such cases, however, the ending -ane ofthe parent alkane is replaced with -adiene, -atriene, etc.

6 Leav-ing the a in the root alkane whenever the first letter of thesuffix is a consonant to make the name easier to we get alkadienes, alkatriens, alkadiynes, 4 Complete the numbering.(a) Number the carbon atoms consecutively from the endof the chain nearer the functional group of the high-est ,5-dimethylhexan-3-one123546O(b)If the same number for the functional group of highest pri-ority is obtained in both directions, the correct IUPAC nameis the one that contains the lowest substituent ,4-dimethylhex-3-ene123546 First substituent has number 2.

7 If we numbered the chainfrom the other side, the first substituent would have num-ber 3.(c) If first substituents occur at an equal distance from eachend of the chain, number from the end nearer a second sub-stituent. If still the same, continue until first point of dif-ference.(E)-2,3,5-trimethylhex-3-ene 123546(d) If numbering from either side gives the same set of locants,number from the end with the substituent that comes firstin alphabetical order.(e) In monosubstituted cycloalkanes and benzene derivatives,the carbon to which the substituent is bonded is alwaysnumber 1.

8 If there is only one substituent, the locant 1 isomitted. However, it is necessary in polysubstituted com-pounds. (f)In polysubstituted cyclic compounds, the starting point andthe direction of numbering are chosen to give lowest lo-cant to the following factors (if present), considered suc-cessively in the order listed below until a decision is reached.(i) The principal functional group named as suffix is alwaysgiven lowest possible number. When the numbering is pre-determined by the nature of the parent hydrocarbon, as inpolycyclic hydrocarbons and heterocyclic compounds, low-est locants are still the rule.

9 Note: When one heteroatom is present in the ring, the lo-cant 1 is attributed to the heteroatom. If two or morekinds of heteroatom occur in the same ring, the number-ing starts from the heteroatom cited first in the followingdescending order: O, S, Se, N, P, As, Sb, Si, Ge, Sn, Pb, B,and Hg. Other heteroatoms get other lowest possiblelocants. 1,2-oxathiolane15423OS 1,3,5-triazine123564 NNNIn the Vol. 83 No. 11 November 2006 Journal of Chemical Education1635(ii) Lowest locant for multiple bonds in cyclic compounds.

10 Note: In Naming cycloalkenes, the double bond is locatedbetween C1 and C2, and the 1 is usually omitted in thename. The ring is numbered clockwise or counterclockwiseto give the first substituent the lower number. However,when a higher seniority functional group is present, the car-bon bonded to such a group becomes C1 and then mul-tiple bonds are considered for lowest possible locants.(iii) Lowest locant for a first substituent (or first point of dif-ference). (iv) If the same numbers will result from numbering in eitherdirection, give the lowest locant for that substituent whichis cited first.