Basic Organic Nomenclature

An Introduction

Dave Woodcock,
Associate Professor Emeritus UBC (Okanagan)
©1996,2000, 2008

4. Functional Groups with Suffix Only

II. Alkynes

Index


The -yne name is given to the C,C triple bond function. The group is linear, as you have seen from the models in the introduction, and may appear anywhere in the carbon chain, thus often requiring a locant (position identifier).

Study the following examples of straight-chain alkynes:

Alkyne StructureIUPAC NameModel
ethyne
propyne
but-1-yne
but-2-yne
pent-1-yne
pent-2-yne
hex-1-yne
hex-2-yne
hex-3-yne

Note from the above names that the locant is only the first number of the two which identify the position of the triple bond. Thus although the triple bond in hex-3-yne is between carbons numbered 3 and 4 in the chain, only the first is required to position the triple bond, the second being understood to be the next higher number.
This observation requires that the triple bond be included in the main chain that is used for the root name and requires a change in the rules for picking the carbon chain used for the root name:

Changes and additions to the rules for naming compounds are thus:

  • the root name is chosen for the longest continuous chain of carbon atoms which contains either the carbon(s) of the functional group or the carbon bearing the functional group.

  • for double or triple C,C bonds, the whole bond must be in the main chain and the locant identifies only the lowest numbered carbon of the two.

  • the functional group is given the lowest possible number.

Note also the position of the locant in the name. IUPAC now puts the locant immediately in front of the group that it is positioning: hex-3-yne rather than 3-hexyne.


Examine the following names for other alkynes:

Alkyne StructureIUPAC NameModel
3-methylbut-1-yne
2,2-dimethylhex-3-yne
3-propylhept-1-yne

Note the last example, which is named as a heptyne: the longest continuous chain of carbons is eight, but this does not contain the functional group.


If more than one C,C triple bond is present, the name can be produced by using diyne, triyne, etc:

Alkyne StructureIUPAC NameModel
oct-2,4-diyne
2,2,9,9-tetramethyldec-3,5,7-triyne

Self-Assessment Problems.
Review Functional Groups with Suffix Only I Introduction

Next page : Functional Groups with Suffix Only III Alkenes.

Index


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