Question

Show how to prepare each compound from 1-heptene. (a) 1,2 -Dichloroheptane (b) 1 -Heptyne (c) 1-Heptanol (d) 2-Octyne (e) cis-2-Octene (f) trans-2-Octene

Short answer

Question: Describe the reactions and reagents involved in synthesizing each of the following compounds from 1-heptene: a) 1,2-Dichloroheptane, b) 1-Heptyne, c) 1-Heptanol, d) 2-Octyne, e) cis-2-Octene, and f) trans-2-Octene. Answer: a) To synthesize 1,2-Dichloroheptane from 1-heptene, perform an addition reaction using Cl2 with the help of UV light or heat. This halogen addition reaction directly generates the desired product. b) To synthesize 1-Heptyne, first perform an addition reaction with HCl to obtain 1-chloroheptane. Then, use NaNH2 as a base to induce an elimination reaction, forming the 1-heptyne product. c) To synthesize 1-Heptanol, carry out an oxymercuration-demercuration reaction on 1-heptene with Hg(OAc)2 and NaBH4 reagents, adding an OH group to the first carbon. d) To synthesize 2-Octyne, first perform a hydrobromination reaction with HBr to obtain 1-heptyl bromide. Then, use NaNH2 to carry out a coupling reaction, forming the 2-octyne product. e) To synthesize cis-2-Octene, first perform a hydrobromination reaction with HBr to obtain 1-heptyl bromide. Next, use KOH as a base to promote an elimination reaction, yielding the cis-2-octene product. f) To synthesize trans-2-Octene, first perform a hydrobromination reaction with HBR to obtain 1-heptyl bromide. Then, use KOt-Bu as a base to promote an elimination reaction, yielding trans-2-octene as the product.

Step-by-step solution

(a) Synthesis of 1,2-Dichloroheptane)

1. Starting from 1-heptene, the first step is to add a chlorine molecule to the double bond: Perform an addition reaction of 1-heptene and Cl\(_{2}\) with the help of UV light or heat to generate 1,2-dichloroheptane directly. The reaction is an example of halogen addition to an alkene, and the UV light or heat provides the required energy to initiate the process.

(b) Synthesis of 1-Heptyne)

1. Conversion to 1-chloroheptane: Perform an addition reaction between 1-heptene and HCl to create 1-chloroheptane. This reaction is another example of halogen addition to an alkene. 2. Conversion to 1-heptyne: Perform an elimination reaction using the reagent NaNH\(_{2}\) on 1-chloroheptane. The reagent is a strong base and will induce the elimination of HCl, generating the 1-heptyne product.

(c) Synthesis of 1-Heptanol)

1. Conversion to 1-heptanol: Perform an oxymercuration-demercuration reaction on 1-heptene using the reagents Hg(OAc)\(_{2}\) and NaBH\(_{4}\). These reagents will add an OH group to the first carbon, creating the desired 1-heptanol product.

(d) Synthesis of 2-Octyne)

1. Conversion to 1-heptyl bromide: Perform a hydrobromination reaction between 1-heptene and HBr to create 1-heptyl bromide. This reaction involves the addition of a bromine atom to the double bond. 2. Conversion to 2-octyne: Perform a coupling reaction using the reagent NaNH\(_{2}\) on 1-heptyl bromide. This treatment leads to the formation of a carbon-carbon bond between two 1-heptyl molecules, creating the desired 2-octyne product.

(e) Synthesis of cis-2-Octene)

1. Conversion to 1-heptyl bromide: Perform a hydrobromination reaction between 1-heptene and HBr to create 1-heptyl bromide, as mentioned previously. 2. Conversion to cis-2-octene: Perform an elimination reaction using the reagent KOH on 1-heptyl bromide. The KOH base will promote the elimination of HBr, generating cis-2-octene as the product.

(f) Synthesis of trans-2-Octene)

1. Conversion to 1-heptyl bromide: Perform a hydrobromination reaction between 1-heptene and HBr to create 1-heptyl bromide, as mentioned previously. 2. Conversion to trans-2-octene: Perform an elimination reaction using the reagent KOt-Bu on 1-heptyl bromide. The KOt-Bu base will promote the elimination of HBr, generating trans-2-octene as the product.