The IUPAC Nomenclature of CH$_3$CH$_2$C(CH$_3$)=C(CH$_3$)$_2$ for the compound is

To determine the IUPAC name of the compound CH$_3$CH$_2$C(CH$_3$)=C(CH$_3$)$_2$, we follow these systematic steps:

1. Analyze the structure

First, let's expand the condensed structural formula to see the carbon chain clearly:

• The chain is: $CH_3 - CH_2 - C(CH_3) = C(CH_3)_2$
• Carbon 1: $CH_3$
• Carbon 2: $CH_2$
• Carbon 3: $C$ (with a $CH_3$ branch)
• Carbon 4: $C$ (with two $CH_3$ branches)

2. Identify the longest carbon chain

We must choose the longest continuous carbon chain that contains the double bond ($C=C$).

• If we count from left to right: $C_1-C_2-C_3=C_4$. This gives us a 5-carbon chain, which is a pentene.

3. Number the chain

Number the chain starting from the end that gives the double bond the lowest possible position number:

• Numbering from the left: The double bond starts at Carbon 2.
• Numbering from the right: The double bond starts at Carbon 2.
• Since both directions give the double bond the position "2", we look at the substituents (the methyl groups). We want the substituents to have the lowest possible locants.
• Numbering from the right (starting at the $C$ with two methyls): • $C_1$ (rightmost $CH_3$) • $C_2$ (the carbon with the double bond) • $C_3$ (the carbon with the double bond and one methyl) • $C_4$ ($CH_2$) • $C_5$ ($CH_3$)

With this numbering, the methyl groups are located at positions 2 and 3.

4. Assemble the name

• Substituents: Two methyl groups at positions 2 and 3 = 2,3-dimethyl
• Parent chain: 5 carbons with a double bond = pent-2-ene
• Full name: 2,3-dimethylpent-2-ene

Conclusion

Comparing this to your options:

• A: 2,3-dimethylpentene (Incomplete, lacks the position of the double bond)
• B: 2,3-dimethylpent-2-ene (Correct)
• C: 3,4-dimethylpent-3-ene (Incorrect numbering)
• D: 3,4-dimethylpentene (Incorrect numbering and incomplete)

Exam Tip: When naming alkenes, always prioritize the double bond. The double bond must be part of the longest chain, and its position number should be as low as possible. If the double bond position is the same from both ends, then prioritize the substituents (the methyl groups) to have the lowest numbers.