Which one of the following reactions will not lead to the desired ether formation in major proportion? (iso-Bu ? isobutyl, sec-Bu ? sec-butyl, nPr ? n-propyl, tBu ? tert-butyl, Et ? ethyl) [2025]

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Q.
Which one of the following reactions will not lead to the desired ether formation in major proportion

(iso-Bu ⇒ isobutyl, sec-Bu ⇒ sec-butyl, nPr ⇒ n-propyl, tBu ⇒ tert-butyl, Et ⇒ ethyl) [2025]

1 ${}^{t}{Bu} \overset{⊝}{O} \overset{\oplus}{N} a + EtBr \to Bu - O - Et$

2

3 4 $iso - Bu \overset{⊝}{O} \overset{\oplus}{N} a + \sec - BuBr \to \sec - Bu - O - iso - Bu$

Ans.
(4)

Williamson ether formation is an $S_{N} 2$ reaction. $S_{N} 2$ reactions give best yield if the attack is on a primary substrate. For secondary substrates, elimination begins to compete with the substitution product, and for tertiary substrates, elimination product is the major product.

Solution

Q.
Which one of the following reactions will not lead to the desired ether formation in major proportion

(iso-Bu ⇒ isobutyl, sec-Bu ⇒ sec-butyl, nPr ⇒ n-propyl, tBu ⇒ tert-butyl, Et ⇒ ethyl) [2025]

1 ${}^{t}{Bu} \overset{⊝}{O} \overset{\oplus}{N} a + EtBr \to Bu - O - Et$

2

3

4 $iso - Bu \overset{⊝}{O} \overset{\oplus}{N} a + \sec - BuBr \to \sec - Bu - O - iso - Bu$

Ans.
(4)

Williamson ether formation is an $S_{N} 2$ reaction. $S_{N} 2$ reactions give best yield if the attack is on a primary substrate. For secondary substrates, elimination begins to compete with the substitution product, and for tertiary substrates, elimination product is the major product.

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Solution

Q. Which one of the following reactions will not lead to the desired ether formation in major proportion (iso-Bu ⇒ isobutyl, sec-Bu ⇒ sec-butyl, nPr ⇒ n-propyl, tBu ⇒ tert-butyl, Et ⇒ ethyl) [2025]

1 ButO⊝N⊕a+EtBr→Bu-O-Et

2

3

4 iso-BuO⊝N⊕a+sec-BuBr→sec-Bu-O-iso-Bu

Ans. (4) Williamson ether formation is an SN2 reaction. SN2 reactions give best yield if the attack is on a primary substrate. For secondary substrates, elimination begins to compete with the substitution product, and for tertiary substrates, elimination product is the major product.

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Q.
Which one of the following reactions will not lead to the desired ether formation in major proportion

(iso-Bu ⇒ isobutyl, sec-Bu ⇒ sec-butyl, nPr ⇒ n-propyl, tBu ⇒ tert-butyl, Et ⇒ ethyl) [2025]

1 ${}^{t}{Bu} \overset{⊝}{O} \overset{\oplus}{N} a + EtBr \to Bu - O - Et$

4 $iso - Bu \overset{⊝}{O} \overset{\oplus}{N} a + \sec - BuBr \to \sec - Bu - O - iso - Bu$

Ans.
(4)

Williamson ether formation is an $S_{N} 2$ reaction. $S_{N} 2$ reactions give best yield if the attack is on a primary substrate. For secondary substrates, elimination begins to compete with the substitution product, and for tertiary substrates, elimination product is the major product.