Consider the
C6 isomers from the previous question.
Two carbon skeletons arise from a
C5 chain and
1 C1 branch.
The centre carbon (C-3) in the C5 chain is different from both C-2 and C-4.
Because the chain is symmetrical about C-3, C-2 and C-4 and equivalent.
Two carbon skeletons arise from a
C4 chain and
two C1 branches.
The C1 units may be either on the same carbon or on different carbons in the C4 chain.
No need to worry about others because this automatically includes
- C4 chain and a C2 branch (red highlighting)
- C3 chain and a C3 branch (pink highlighting)
- C3 chain, one C1 branch and one C2 branch (green highlighting)