What is the IUPAC name of CH3CCI=C(CH3)2?

Step 1: Analyze the structure

CH3–CCl=C(CH3)2

• Carbon 1: CH3
• Carbon 2: C with Cl, double bonded to C3
• Carbon 3: C with two CH3 groups (one is in the main chain as C4, the other is a branch)

Step 2: Find the longest chain containing the double bond

CH3–C(Cl)=C(CH3)–CH3 is 4 carbons, so the parent is butene.

Step 3: Number the chain

Numbering from the left gives the double bond at C2 (C2=C3). Numbering from the right gives it at C3, which is worse. So we number from the left:

• C1: CH3
• C2: C–Cl (double bond starts here)
• C3: C–CH3 (methyl branch)
• C4: CH3

Step 4: Name the substituents

• Chloro at C2
• Methyl at C3
• Double bond at C2

Substituents are listed alphabetically (chloro before methyl): 2-chloro-3-methylbut-2-ene

Step 5: Check the options

• A and E use "yne", which means a triple bond, so they are wrong.
• C leaves out the position of the double bond, so it is incomplete.
• D lists the substituents in the wrong order, since the substituents should be alphabetical (chloro before methyl).
• B is "2-chloro-3-methylbut-2-ene". The spelling "ene" is written loosely, but it matches the correct name.

Answer: B

Tip: Name alkenes in this order: (1) find the longest chain containing the double bond, (2) number so the double bond gets the lowest number, (3) list substituents alphabetically. Remember that "yne" means a triple bond, so you can eliminate those options right away.