This is the list of structural isomers of nonane. There are 35.

Straight-chain Nonane

Octanes 2-Methyloctane 3-Methyloctane 4-Methyloctane

Heptanes Isomers where heptane is the longest chain Dimethyl 2,2-Dimethylheptane 2,3-Dimethylheptane 2,4-Dimethylheptane 2,5-Dimethylheptane 2,6-Dimethylheptane 3,3-Dimethylheptane 3,4-Dimethylheptane 3,5-Dimethylheptane 4,4-Dimethylheptane

Ethyl 3-Ethylheptane 4-Ethylheptane

Hexane Isomers where hexane is the longest chain include: Trimethyl 2,2,3-Trimethylhexane 2,2,4-Trimethylhexane 2,2,5-Trimethylhexane 2,3,3-Trimethylhexane 2,3,4-Trimethylhexane 2,3,5-Trimethylhexane 2,4,4-Trimethylhexane 3,3,4-Trimethylhexane

Ethyl+Methyl 3-Ethyl-2-methylhexane 4-Ethyl-2-methylhexane 3-Ethyl-3-methylhexane 3-Ethyl-4-methylhexane

Pentane Isomers where pentane is the longest chain include: Tetramethyl 2,2,3,3-Tetramethylpentane 2,2,3,4-Tetramethylpentane 2,2,4,4-Tetramethylpentane 2,3,3,4-Tetramethylpentane

Ethyl+Dimethyl 3-Ethyl-2,2-dimethylpentane 3-Ethyl-2,3-dimethylpentane 3-Ethyl-2,4-dimethylpentane

Diethyl 3,3-Diethylpentane

References