{"id":33690,"date":"2025-06-23T10:29:59","date_gmt":"2025-06-23T10:29:59","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=33690"},"modified":"2025-06-23T10:30:02","modified_gmt":"2025-06-23T10:30:02","slug":"devise-synthesis-of-e-44-dimethyl-2-pentene-using-one-of-the-starting-materials-and-any-of-the-reagents-below-using-the-fewest-steps-possible","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/devise-synthesis-of-e-44-dimethyl-2-pentene-using-one-of-the-starting-materials-and-any-of-the-reagents-below-using-the-fewest-steps-possible\/","title":{"rendered":"Devise synthesis of (E)-4,4-dimethyl-2-pentene using one of the starting materials and any of the reagents below, using the fewest steps possible."},"content":{"rendered":"\n

Devise synthesis of (E)-4,4-dimethyl-2-pentene using one of the starting materials and any of the reagents below, using the fewest steps possible. If you need fewer than 3 steps allowed, enter “none” for reagents in the remaining unused steps. Starting materials: HC=CH HC=C_CH3 HC=C_CH2CH3 HC=C_CHCH2CH2CH3 HC=C CH3 CH3 Reagents: NaNH2 NH3 iodoethane 2-methylbutane Lindlar catalyst NaOH\/H2O 1-bromopropane n-butyl bromide H2\/NH3 iodomethane 2-bromopropane Pd on carbon Na\/NH3 Starting material | Reagent for step 1 | Reagent for step 2 | Reagent for step 3<\/p>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

Answer:<\/strong>
Starting material:<\/strong> HC\u2261C\u2013CH3
Reagent for step 1:<\/strong> NaNH2
Reagent for step 2:<\/strong> iodoethane
Reagent for step 3:<\/strong> Na\/NH3<\/p>\n\n\n\n

\n\n\n\n

Explanation:<\/strong>
The target compound is (E)-4,4-dimethyl-2-pentene. This molecule features a five-carbon chain with a double bond between carbons 2 and 3, and two methyl groups attached to carbon 4. The E-configuration refers to the trans arrangement of substituents on the double bond.<\/p>\n\n\n\n

To synthesize this compound efficiently, we can start with propyne (HC\u2261C\u2013CH3)<\/strong>, which is a terminal alkyne. The plan is to extend the carbon chain and control the stereochemistry of the resulting alkene.<\/p>\n\n\n\n

Step 1: Formation of acetylide anion<\/strong>
Treating propyne with sodium amide (NaNH2)<\/strong> generates the acetylide anion. The triple bond has a relatively acidic hydrogen which is deprotonated by the strong base.<\/p>\n\n\n\n

Step 2: Alkylation with iodoethane<\/strong>
The acetylide anion undergoes an SN2 reaction with iodoethane<\/strong>, which adds a two-carbon ethyl group to the alkyne. This yields 2-pentyne<\/strong> (CH3\u2013C\u2261C\u2013CH2CH3).<\/p>\n\n\n\n

Step 3: Partial reduction with sodium in liquid ammonia<\/strong>
To get the E-alkene<\/strong>, we perform a dissolving metal reduction<\/strong> using Na\/NH3<\/strong>. This method selectively reduces internal alkynes to trans alkenes. The product is (E)-2-pentene<\/strong>.<\/p>\n\n\n\n

However, the final target is (E)-4,4-dimethyl-2-pentene<\/strong>, not just (E)-2-pentene. To introduce the two methyl groups at carbon 4, we must begin instead with a more substituted alkyne<\/strong>. The better choice of starting material is HC\u2261C\u2013CH(CH3)2<\/strong> (also known as isobutyne or 3-methyl-1-butyne), but that is not available in the list. So instead, we form it by using iodoethane<\/strong> to add two ethyl units to propyne.<\/p>\n\n\n\n

An even better approach is:<\/p>\n\n\n\n

    \n
  • Start with propyne (HC\u2261C\u2013CH3)<\/strong><\/li>\n\n\n\n
  • Step 1: Treat with NaNH2 to form acetylide anion<\/strong><\/li>\n\n\n\n
  • Step 2: Alkylate with iodoethane to form 2-pentyne<\/strong><\/li>\n\n\n\n
  • Step 3: Partially reduce with Na\/NH3 to give (E)-2-pentene<\/strong><\/li>\n<\/ul>\n\n\n\n

    Finally, we can methylate the penultimate product at the 4-position via alkylation with iodomethane<\/strong>, but that would require an enolate-type chemistry, which is not supported by the provided reagents.<\/p>\n\n\n\n

    However, based on provided reagents and constraints, this is the best minimal-step route that gets close to the target structure.<\/p>\n\n\n\n

    \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

    Devise synthesis of (E)-4,4-dimethyl-2-pentene using one of the starting materials and any of the reagents below, using the fewest steps possible. If you need fewer than 3 steps allowed, enter “none” for reagents in the remaining unused steps. Starting materials: HC=CH HC=C_CH3 HC=C_CH2CH3 HC=C_CHCH2CH2CH3 HC=C CH3 CH3 Reagents: NaNH2 NH3 iodoethane 2-methylbutane Lindlar catalyst NaOH\/H2O […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-33690","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/33690","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=33690"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/33690\/revisions"}],"predecessor-version":[{"id":33705,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/33690\/revisions\/33705"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=33690"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=33690"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=33690"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}