Which of the following is the correct IUPAC name of given organic compound (X)?

Solution

Chemistry ma’am · 3 steps

The CH₂Br carbon is part of the main chain, so start counting from it.

1. Pick the chain. The longest chain that contains the double bond runs CH₃-CH=C-CH₂Br. That is 4 carbons, so the parent is butene. The CH₂ holding Br is a chain carbon, and Br is the substituent on it.

   Numbering from	Double bond	Substituents	Locant set
   CH₂Br end	C2	1-bromo, 2-methyl	{1, 2}
   CH₃ end	C2	3-methyl, 4-bromo	{3, 4}

2. Break the tie. The double bond gets locant 2 from either end, so it cannot decide the direction. The substituents then need the lowest set, and {1, 2} beats {3, 4}.
3. So. Bromo and methyl are written in alphabetical order, giving 1-Bromo-2-methylbut-2-ene, option (b).

The idea to keep. Number first for the lowest locant on the double bond. If both ends tie, give the lowest locants to the substituents, and do not leave out a carbon that carries a halogen.

Answer from the NTA final answer key. Solution by PrepWiser.