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what is the iupac name of this compound? (chemical structure: h₃c-c(=c)…

Question

what is the iupac name of this compound?

(chemical structure: h₃c-c(=c)-ch₂ch₃ with h on each c)

options:

  • cis-3-pentene
  • cis-2-pentene
  • ethylpropene
  • 1-methyl-2-ethylpentene
  • trans-3-pentene

Explanation:

Brief Explanations
  1. First, identify the parent chain: The longest carbon chain with the double bond has 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 left, carbons are 1 - 5: \( \ce{C1(H3C)-C2(=C)-C3(CH2CH3)} \), but numbering should make the double bond at the lowest position. Wait, actually, the double bond is between C2 and C3? Wait, no: let's draw the structure: \( \ce{H3C - CH=CH - CH2CH3} \)? Wait, no, the given structure is \( \ce{H3C - C(H)=C(H) - CH2CH3} \). So the carbon chain is 5 carbons (pentene). The double bond is between carbon 2 and 3? Wait, no, numbering from the left: C1 is \( \ce{H3C} \), C2 is \( \ce{C(H)=} \), C3 is \( \ce{=C(H) - CH2CH3} \)? Wait, no, the correct numbering: the double bond is between C2 and C3? Wait, no, let's count the carbons: the main chain has 5 carbons (pent-). The double bond is at position 2 (since numbering from the left, the double bond is between C2 and C3? Wait, no, \( \ce{H3C - C(H)=C(H) - CH2CH3} \): C1: \( \ce{H3C} \), C2: \( \ce{C(H)=} \), C3: \( \ce{=C(H) - CH2CH3} \)? Wait, no, the \( \ce{CH2CH3} \) is on C3? Wait, no, the structure is \( \ce{H3C - C(H)=C(H) - CH2CH3} \), so the carbon chain is C1 (H3C), C2 (double bond with C3), C3 (double bond with C2 and attached to CH2CH3? No, \( \ce{CH2CH3} \) is a group on C3? Wait, no, the structure is \( \ce{H3C - C(H)=C(H) - CH2CH3} \), so the main chain is 5 carbons: C1 (H3C), C2 (C with H and double bond), C3 (C with H and double bond and CH2CH3? No, \( \ce{CH2CH3} \) is a group on C3? Wait, no, \( \ce{CH2CH3} \) is ethyl, so C3 is attached to ethyl? Wait, no, the structure is \( \ce{H3C - C(H)=C(H) - CH2CH3} \), so the carbon atoms are: C1: \( \ce{H3C} \), C2: \( \ce{C(H)=} \), C3: \( \ce{=C(H) - CH2CH3} \)? No, that's not right. Wait, the correct way: the double bond is between C2 and C3? Wait, no, let's write the formula: \( \ce{C5H10} \) (since it's a pentene). The structure is \( \ce{H3C - CH=CH - CH2CH3} \)? Wait, no, the given structure has \( \ce{H3C} \) on one C, \( \ce{CH2CH3} \) on the other, with H on both carbons of the double bond. So the two substituents on the double bond carbons: on C2 (attached to \( \ce{H3C} \) and H) and C3 (attached to \( \ce{CH2CH3} \) and H). So the double bond is between C2 and C3? Wait, no, numbering from the left, C1 is \( \ce{H3C} \), C2 is the next, C3 is the one with \( \ce{CH2CH3} \). Wait, no, the correct numbering is to give the double bond the lowest possible number. So the double bond is between C2 and C3? Wait, no, \( \ce{H3C - CH=CH - CH2CH3} \) is 2 - pentene? Wait, no, \( \ce{H3C - CH=CH - CH2CH3} \) has the double bond at position 2 (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 larger groups (methyl on C2 and ethyl on C3) are on opposite sides? Wait, no, in cis isomer, the two similar groups (H in this case) are on the same side. Wait, the two carbons of the double bond: C2 has \( \ce{H3C} \) and H, C3 has \( \ce{CH2CH3} \) and H. So the H atoms are on the same side (cis), and the double bond is at position 2. So the name is cis - 2 - pentene. Let's check the options:
  • cis - 3 - pentene: double bond at 3, but numbering should be lower, so 2 is better.
  • cis - 2 - pentene: matches.
  • ethylpropene: incorrect, parent chain is pentene, not propene.
  • 1 - methyl - 2 - ethylpentene: incorrect, parent chain is pentene, no need for methyl and ethyl as substituents (the main chain is 5 carbons).
  • trans - 3 - penten…

Answer:

B. cis - 2 - pentene