s we have learned, IRnyis ictate by wp ters, bond strength and reduced mass (a).
ID: 304016 • Letter: S
Question
s we have learned, IRnyis ictate by wp ters, bond strength and reduced mass (a). hybridization states also impact on wavenu ed by tw nd of absorption (b) constant (bond strength mim2 uced mass Hybridized atomic orbitais C-H 100% s character -3100 cm1 -3300 cm-1 s characterscharacted s charact -2900 cm1 It has been well-known that decreasing ring size shifts carbonyl absorbance to higher frequencies. following statements is true? Which of the 1815 cm- 1780 cm1 1745 cm-1 1715 cm1 1705 cm1 increase ring-strain a) A C-O double bond in cyclopropanone A is the longest bond. b) A C-O double bond in cyclopropane A has the highest s character. c) The reduced mass primarily impacts on the trend. d) A C-O double bond in cyclohexanone D is the highest p character. e) A C-O double bond in cycloheptanone E is the strongest bond.Explanation / Answer
With the decrease of ring size the force constant of C=O bond increases and frequency of adsorption increases.
Smaller rings have more p character in their ring bonds and the bond outside the ring have more s character. This increase in the s character of C=O double bond and strengthened the bond which finally increases the C=O stretching frequency .
An alternate explanation is that, C=O stretching frequency is affected by adjacent C-C bond stretching. When a ring has smaller size it is in strain then the interaction between C-C bond and C=O double bond increases the energy need to produce C=O stretching as a result C=O stretching frequency increases.
Hence, the right answer is option b.
A C=O double bond in cyclopropane A has the highest s character.
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