Which of the following would have the lowest stretching frequency
A. C=C
B. C-O
C. C=O
D. N=O
E. C-H
To determine which of the following options would have the lowest stretching frequency, we need to consider the bond strength and the force constant of each bond. The stretching frequency of a bond is inversely proportional to its bond strength and directly proportional to its force constant.
The bond strength refers to the energy required to break the bond, while the force constant represents the stiffness or rigidity of the bond. A higher bond strength and a lower force constant will result in a lower stretching frequency.
Let's analyze each option:
A. C=C:
A carbon-carbon double bond (C=C) typically has a higher bond strength than a carbon-oxygen (C-O) or carbon-nitrogen (C-N) bond because it involves more electron density. Additionally, a C=C bond is usually more rigid than a C-O or C-N bond because of the sp2 hybridization of the carbon atoms. Therefore, the stretching frequency of the C=C bond would typically be higher than the other options.
B. C-O:
A carbon-oxygen (C-O) bond generally has a lower bond strength compared to a C=C bond because oxygen is more electronegative than carbon, leading to a larger dipole moment and weaker bond. The force constant of a C-O bond is typically lower than that of a C=C bond because the C-O bond is often more flexible due to the sp3 hybridization of carbon. Consequently, the stretching frequency of the C-O bond is usually higher than the C=C bond but lower than other options such as C=O or N=O.
C. C=O:
A carbon-oxygen double bond (C=O) usually has a higher bond strength than a C-O bond because it involves more electron density. The force constant of a C=O bond is also higher than that of a C-O bond due to the sp2 hybridization of carbon. Therefore, the stretching frequency of the C=O bond is higher than the C=C and C-O bonds.
D. N=O:
A nitrogen-oxygen double bond (N=O) typically has a higher bond strength than a C-O bond. The force constant of a N=O bond is also higher due to the resonance stabilization of the nitro group. Therefore, the stretching frequency of the N=O bond would generally be higher than the C=C, C-O, and C=O bonds.
E. C-H:
A carbon-hydrogen (C-H) bond generally has the lowest bond strength among the options listed. The force constant of a C-H bond is typically lower because it has a lower rigidity compared to double or triple bonds. Consequently, the stretching frequency of the C-H bond would typically be the lowest among the given options.
Therefore, option E, C-H, would have the lowest stretching frequency.