Question

what are stretching vibrations ? Explain with figure the vibration of CH2 molecule.​

Answer 1

Answer:

A stretching vibration changes the bond length. There are two types of stretching vibrations. In symmetric stretching, two or more bonds vibrate in and out together. . In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.

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molecular vibration is a periodic motion of the atoms of a molecule relative to each other, such that the center of mass of the molecule remains unchanged. The typical vibrational frequencies, range from less than 1013 Hz to approximately 1014 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm−1.

In general, a non-linear molecule with N atoms has 3N – 6 normal modes of vibration, but a linear molecule has 3N – 5 modes, because rotation about the molecular axis cannot be observed.A diatomic molecule has one normal mode of vibration, since it can only stretch or compress the single bond. Vibrations of polyatomic molecules are described in terms of normal modes, which are independent of each other, but each normal mode involves simultaneous vibrations of different parts of the molecule.

A molecular vibration is excited when the molecule absorbs energy, ΔE, corresponding to the vibration's frequency, ν, according to the relation ΔE = hν, where h is Planck's constant. A fundamental vibration is evoked when one such quantum of energy is absorbed by the molecule in its ground state. When multiple quanta are absorbed, the first and possibly higher overtones are excited.

Answer 2

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• Stretching: a change in the length of a bond, such as C–H or C–C.
• Bending: a change in the angle between two bonds, such as the HCH angle in a methylene group.
• Rocking: a change in angle between a group of atoms, such as a methylene group and the rest of the molecule.

• A stretching vibration changes the bond length.
• There are two types of stretching vibrations. In symmetric stretching, two or more bonds vibrate in and out together.
• In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer