Organic Chemistry: Cyclic compounds, Alkenes and Alkynes

Cycloalkanes

Name / Formula / Condensed Structural Formula / Line Diagram
Cyclopropane / C3H6
Cyclobutane / C4H8
Cyclopropane / C5H10
Cyclohexane / C6H12

Rule 1. Determine the parent. Count the number of carbon atoms in the ring and also in the largest alkyl substituent.

a)If the number of carbon atoms in the ring is equal to or greater than the number in the largest substituent, the compound is named as an alkyl-substituted cycloalkane (see Example 1). If the number of carbon atoms in the ring is less than the number of carbon atoms in the substituent, it is named as a cycloalkyl-substituted alkane (see Example 2).

Rule 2. Number and name the substituents. If two or more substituents are on a cycloalkane, start C-1 at a point of attachment such that that the second substituent has as low a number as possible.

Alkenes

Alkenes have at least one double bond. The general formula is: CnH2n

The rules for naming alkenes

1)The longest or parent chain must contain a double bond and the chain is numbered from the end closest to the multiple bond

2)The name of the parent chain of the compound is preceded by a number that indicates the position of the multiple bond on the parent chain.

Ex. 1) 1- butene vs 2 butene

3)The name of any branch (alkyl group) is preceded by a number that indicates the position of the branch on the parent chain (the same procedure as that used with alkanes).

Ex.2) 2-methyl-1-butene

Ex 3) 2, 5-dimethyl-2-hexene

ALKYNES

These have at least one triple bond. The general formula is:

Nomenclature of alkynes follows the same rules as that of alkenes but have no cis/trans isomerism. Organic compounds with double and triple bonds are said to be UNSATURATED because fewer atoms are attached the carbon atom framework than the number that could be attached if all the bonds were single. Therefore ______and ______are unsaturated organic compounds and alkanes are ______.

Ex 1)Ex 2)

Ex 3) 4–methyl– 1–pentyne

Ex 4) 3,3-dimethyl-1-butyne

Cycloalkenes and cycloalkynes

Double and triple bonds can also occur in ring structures. To name these, number the carbons in the ring such that the substituents have the lowest possible number.

Ex.

Aromatic Compounds

A six carbon cyclic molecule that contains 3 double bonds is called benzene. Molecules with this special type of electron sharing are called aromatic compounds. (CnHn)

Benzenemethylbenzene (toluene)

1