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(a)
Interpretation:
The CN stretching mode that absorbs the higher-frequency IR photons is to be indicated for given pair of compounds. The reason for it is to be explained.
Concept introduction:
We simplify the picture of molecular vibrations by considering the ball-and-spring model, which treats bonds as simple springs that connect atoms together. According to Hooke’s law, the spring vibrates at a particular frequency (
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Answer to Problem 15.19P
The CN stretching mode that absorbs the higher-frequency IR photons due to strong and stiffer bond is indicated below,
Explanation of Solution
The given pair of compounds is,
The triple bonds tend to be stronger and stiffer than double bonds. A stronger and stiffer bond tends to lead to a higher vibrational frequency. In given pair of compounds, with the faster vibration, the
The CN stretching mode that absorbs the higher-frequency IR photons is shown below,
The CN stretching mode that absorbs the higher-frequency IR photons is indicated on the basis of the relationship between strength and stiffness of the bond and vibrational frequency.
(b)
Interpretation:
The CN stretching mode that absorbs the higher-frequency IR photons is to be indicated for given pair of compounds. The reason for it is to be explained.
Concept introduction:
We simplify the picture of molecular vibrations by considering the ball-and-spring model, which treats bonds as simple springs that connect atoms together. According to Hooke’s law, the spring vibrates at a particular frequency (

Answer to Problem 15.19P
The CN stretching mode that absorbs the higher-frequency IR photons due to strong and stiffer bond is indicated below,
Explanation of Solution
The given pair of compounds is,
The double bonds tend to be stronger and stiffer than single bonds. A stronger and stiffer bond tends to lead to a higher vibrational frequency. In given pair of compounds, with the faster vibration, the
The CN stretching mode that absorbs the higher-frequency IR photons is shown below,
The CN stretching mode that absorbs the higher-frequency IR photons is indicated on the basis of the relationship between strength and stiffness of the bond and vibrational frequency.
(c)
Interpretation:
The CN stretching mode that absorbs the higher-frequency IR photons is to be indicated for given pair of compounds. The reason for it is to be explained.
Concept introduction:
We simplify the picture of molecular vibrations by considering the ball-and-spring model, which treats bonds as simple springs that connect atoms together. According to Hooke’s law, the spring vibrates at a particular frequency (

Answer to Problem 15.19P
The CN stretching mode that absorbs the higher-frequency IR photons due to lower mass is indicated below,
Explanation of Solution
The given pair of compounds is,
In both compounds there is
But
The CN stretching mode that absorbs the higher-frequency IR photons is shown below,
The vibrational mode that absorbs at a higher frequency in the IR region is determined on the basis of the relationship between mass and vibrational frequency.
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Chapter 15 Solutions
Organic Chemistry: Principles and Mechanisms (Second Edition)
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