Question

what is the iupac name of this compound?
h₃c
|
c=c
| |
h h
|
ch₂ch₃
options: cis-3-pentene, cis-2-pentene, ethylpropene, 1-methyl-2-ethylpentene, trans-3-pentene

Explanation:

1. First, identify the parent chain: The longest carbon chain with the double bond is 5 carbons (pentene).
2. Locate the double bond: The double bond is between carbon 2 and 3 (numbering to give the double bond the lowest number, so from the left, carbons are numbered 1 - 5: C1 (H₃C), C2 (with H and double bond), C3 (with H and CH₂CH₃), C4, C5? Wait, no, let's re - number. The correct numbering: the double bond is between C2 and C3. Wait, the structure is H₃C - C(H)=C(H)-CH₂CH₃. So the parent chain is pentene (5 carbons). The double bond is at position 2 (since numbering from the left: C1: H₃C, C2: C with H and double bond, C3: C with H and CH₂CH₃, C4: CH₂, C5: CH₃? Wait, no, the chain is H₃C - C = C - CH₂ - CH₃. So carbons are 1 (H₃C), 2 (C with H), 3 (C with H), 4 (CH₂), 5 (CH₃)? Wait, no, the CH₂CH₃ is a group on C3? Wait, no, the structure is H₃C - C(H)=C(H)-CH₂CH₃. So the carbon chain is 5 carbons: C1 (H₃C), C2 (C =), C3 (C =), C4 (CH₂), C5 (CH₃)? No, wait, CH₂CH₃ is a group, so the main chain is 5 carbons: H₃C - C - C - CH₂ - CH₃ with a double bond between C2 and C3. Now, check the stereochemistry: the two H atoms are on the same side of the double bond (cis) because the two substituents on C2 are H and CH₃, and on C3 are H and CH₂CH₃. The similar groups (H) are on the same side, so it's cis. And the double bond is at position 2 (since numbering to give the double bond the lowest number: if we number from the left, double bond at C2 - C3; if from the right, it would be C3 - C4, so left numbering is better). So the name is cis - 2 - pentene.

Answer:

B. cis - 2 - pentene