Chapter 14: Q62P (page 527)

The reaction of \({\left( {{\bf{C}}{{\bf{H}}_{\bf{3}}}} \right)_{\bf{3}}}{\bf{CCHO}}\) with \({\left( {{{\bf{C}}_{\bf{6}}}{{\bf{H}}_{\bf{5}}}} \right)_{\bf{3}}}{\bf{P = C}}\left( {{\bf{C}}{{\bf{H}}_{\bf{3}}}} \right){\bf{OC}}{{\bf{H}}_{\bf{3}}}\), followed by treatment with aqueous acid, afford R \(\left( {{{\bf{C}}_{\bf{7}}}{{\bf{H}}_{{\bf{14}}}}{\bf{O}}} \right)\). R has strong absorption in its IR spectrum at 1717 \({\bf{c}}{{\bf{m}}^{{\bf{ - 1}}}}\) and three singlets in its \({}^{\bf{1}}{\bf{H}}\)-NMR spectrum at 1.02 (9 H), 2.13 (3 H), and 2.33 (2 H) ppm. What is the structure of R? We will learn about this reaction in Chapter 21.

Short Answer

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Step by step solution

Wittig reaction

The olefination reaction involving the conversion of a carbonyl compound into an alkene using the triphenylphosphonium ylide is known as the Wittig reaction.

Analysing the data

Given data:

Chemical formula =\({{\rm{C}}_7}{{\rm{H}}_{{\rm{14}}}}{\rm{O}}\)

IR absorption at = 1717 \({\rm{c}}{{\rm{m}}^{{\rm{ - 1}}}}\)

\({}^{\rm{1}}{\rm{H}}\)-NMR spectra = 1.02 ppm (9H), 2.13 ppm (3H), 2.33 ppm (2H)

The degree of unsaturation (IHD) \({\rm{ = }}\frac{{\left( {\left( {{\rm{2n + 2}}} \right){\rm{ - x}}} \right)}}{{\rm{2}}}\),

where

n= number of carbon atoms

x= (Number of hydrogen atoms) + (Number of halogen atoms) - (Number of nitrogen atoms)

On substituting the values,

the degree of unsaturation (IHD) \(\begin{aligned}{c} = \frac{{\left( {\left( {{\rm{2}} \times 7{\rm{ + 2}}} \right){\rm{ - 14}}} \right)}}{{\rm{2}}}\\ = 1\end{aligned}\).

The value of IHD indicates the presence of a pi-bond.

The singlet at 1.02 ppm attributes to 9H having a neighboring carbon with no hydrogen atoms.