Unsaturated fatty acids are often classified according to the number of carbon atoms between the terminal methyl carbon (the omega carbon) and the closest double bond to the methyl end of the chain. An omega‑3 fatty acid, for example, would have a double bond in position 3 counting from the methyl end of the molecule. Identify which omega class each fatty acid belongs to.

(1) Palmitoleic acid

(2) Oleic acid

(3) Linoleic acid

(4) Arachidonic acid

(A) Omega 3

(B) Omega 7

(C) Omega 6

(D) Omega 9

(1) Palmitoleic acid - (B) Omega 7

(2) Oleic acid - (D) Omega 9

(3) Linoleic acid - (C) Omega 6

(4) Arachidonic acid - (C) Omega 6

Explanation:

For unsaturated fatty acids, we can calculate the omega class with the following expression:

omega class = total number of carbons - position of the double bond closest to the omega carbon

(1) Palmitoleic acid

IUPAC name: (9Z) - hexadec-9-enoic acid

Total number of carbons: 16

Position of the double bond closest to the omega carbon: 9

Omega class: 7

(2) Oleic acid

IUPAC name: (9Z) - Octadec-9-enoic acid

Total number of carbons: 18

Position of the double bond closest to the omega carbon: 9

Omega class: 9

(3) Linoleic acid

IUPAC name: (9Z, 12Z) - octadeca-9,12-dienoic acid

Total number of carbons: 18

Position of the double bond closest to the omega carbon: 12

Omega class: 6

(4) Arachidonic acid

IUPAC name: (5Z, 8Z, 11Z, 14Z) - 5,8,11,14-Eicosatetraenoic acid

Total number of carbons: 20

Position of the double bond closest to the omega carbon: 14

Omega class: 6