Question

1.) Infrared spectroscopy relies on what phenomenon? A.) electronic transitions B.) molecular rotations C.) nuclear alignments D.) molecular stretching and bending E.) conformational interconversion

14.) The IR spectrum of which type of compound generally exhibits evidence of hydrogen bonding? A.) Aldehyde B.) Carboxylic Acid C) Alkene D.) Ester E.) Ketone

16.) An anticitpated IR absorption band may not be observed because... A.) it occurs outside the range of the instrument used. B.) no change occurs in the dipole moment during the vibraton. C.) the absorption band is eclipsed by another. D.) the intensity is so weak that it cannot be differentiated from instrument noise. E.) all of these choicies

18.) The IR spectrum of which type of compound will not show evidence of hydrogen bonding? A.) Aldehyde B.) Alcohol C.) Carboxylic Acid D.)Phenol E.) Primamary amine

Answer 1

Ans 1) D.) molecular stretching and bending

Reason: IR works on the priciple of change in dipole moment in a molecule when subjected to IR radiations. During this change, the bond stretches and bends in various ways reulting into IR value.

Ans 14) B.) Carboxylic Acid

Reason: Carboxylic Acid consists of hydrogen bonding which is exhibted in IR. The hydrogen bonded -OH appears as broad signal in the region of 3450-3300 cm-1.

Ans 16) B.) no change occurs in the dipole moment during the vibraton.

Reason: IR is based on the principle of change in dipole moment. SO if no change is there in dipole moment, IR is not observed.

Ans 18) A.) Aldehyde

Reason: All the rest compounds have hydrogen bonding and appear as broad signal in the region of 3450-3300 cm-1. But in aldehyde there is no hydrogen bond.