Question

What factors govern the position of an IR absorption peak? Select one or more correct answers.

(A) strength of the bond
(B) effect of a magnetic field on nucleus spin
(C) masses of the atoms involved in the bond
(D) the type of vibration being observed

Answer 1

The position of an IR absorption peak is determined by the strength of the bond, the masses of the atoms involved in the bond, and the type of vibration being observed. So the correct options are A, C, and D.

Step-by-step explanation:

The factors governing the position of an IR absorption peak are:

• (A) strength of the bond
• (C) masses of the atoms involved in the bond
• (D) the type of vibration being observed

The strength of a bond influences the frequency at which it will absorb IR radiation; strong bonds require more energy to vibrate and thus absorb at higher frequencies. The masses of the atoms in a bond affect its vibrational frequency as well, following the principle that lighter atoms vibrate at higher frequencies compared to heavier ones. Lastly, the type of vibration (stretching, bending, etc.) largely determines the energy level of the absorption peak. The vibrational mode must result in a change in the dipole moment of the molecule to be IR active, with more polar bonds showing stronger IR absorption.

Answer 2

The factors that govern the position of an IR absorption peak are:

(A) strength of the bond

(C) masses of the atoms involved in the bond

(D) the type of vibration being observed

Step-by-step explanation:

In infrared spectroscopy the molecules absorb the frequencies that are characteristic of their structure. These absorptions occur at resonance frequencies, that is, the frequency of the absorbed radiation coincides with the frequency of vibration. The energies are affected by the shape of molecular potential energy surfaces, the masses of atoms and the associated vibronic coupling. The resonance frequencies are also related to the strength of the bond and the mass of the atoms at each end of it. Therefore, the frequency of vibrations is associated with a particular normal movement mode and a particular type of link.