Answer
(a) 2-methylpentane
(b) 2,3,4-trimethylhexane
(c) 3-ethylhexane
(d) 3-methyl-1,4-pentadiene
(e) 2-pentyne
(f) 3-phenyl-1-pentene
Work Step by Step
(a) This is an alkane.
-- Step 1: We need to find the longest contineuous carbon chain (LCCC), which is shown in the box in the image below. This LCCC has 5 carbons, so the parent part is pentane.
-- Step 2: We number the LCCC from the side closer to the alkyl substituent. In this case, we number from the left.
-- Step 3: We put the position and the name of the alkyl substituent right before the parent part, so the compound's name is 2-methylpentane.
(b) This is an alkane as well.
-- Step 1: The longest contineuous carbon chain (LCCC), which is shown in the box in the image below, has 6 carbons instead of 5. So, the parent part is hexane.
-- Step 2: We number the LCCC from the side so that the position numbers of the three aklyl substituents can be the possible lowest. If we number from left, we would get 3.4,5 and if we number from right, we would get 2,3,4. In this case, we should number from the right.
-- Step 3: We put the positions and the names of the alkyl substituents right before the parent part, so the compound's name is 2,3,4-trimethylhexane.
(c) This is an alkane as well.
-- Step 1: The longest contineuous carbon chain (LCCC), which is shown in the box in the image below, has 6 carbons instead of 5. So, the parent part is hexane.
-- Step 2: We number the LCCC from the side closer to the alkyl group substituent. In this case, we should number in the way shown in the image below.
-- Step 3: We put the position and the name of the alkyl substituent right before the parent part, so the compound's name is 3-ethylhexane.
(d) This is an alkene.
-- Step 1: We need pick the longest continuous carbon chain (LCCC) containing all the double bonds, which is shown in the box in the image below. It has 5 carbons and two double bonds, so the parent part is pentadiene.
-- Step 2: We number the LCCC from the side so that the position numbers of the two double bonds can be the possible lowest. However, no matter whether we number from left or from right, we would get 1,4 for the positions of the double bonds. So then, we number from the side closer to the alkyl substituent. And regardless of whether we number from left or from right, we would get 3 for the position of the alkyl substituent.
-- Step 3: We put the position and the name of the alkyl substituent, as well as the position of double bonds before the parent part (pentadiene). So the compound's name is 3-methyl-1,4-pentadiene.
(e) This is an alkyne.
-- Step 1: This alkyne has 5 carbons and one triple bond, so the parent part is pentyne.
-- Step 2: As shown by the image below, we number the carbon chain from the side closer to the triple bond, which is from the left.
-- Step 3: We put the position of triple bond right before the parent part, so the compound's name is 2-pentyne.
(f) This is an alkene.
-- Step 1: The longest continuous carbon chain (LCCC) containing all the double bond(s), which is shown in the box in the image below, has 5 carbons and one double bond, so the parent part is pentene.
-- Step 2: We number the LCCC from the side closer to the double bond, so we should number from right. Notice in naming the LCCC of an alkene, double bond(s) have/has priority over the alkyl substituents.
-- Step 3: We put the position and the name of the alkyl substituent, as well as the position of double bond before the parent part (pentene). So the compound's name is 3-phenyl-1-pentene.
