Chapter U2, Problem C7.5RE

Interpretation Introduction

Interpretation : The relation between the molecular shape and smell is to be explained.

Concept Introduction :

Molecules smell differently. The chemistry behind smell is very complicated. There are many ways by which one can predict smell of a compound. These are molecular formula, functional group, chemical name and overall shape of the molecule. A molecule’s shape is most important factor related to smell.

Answer to Problem C7.5RE

Besides molecular structure, shape of molecule is also related to smell. Molecular shape is determined by the bonds present between atoms and location of electrons. Different molecular shapes have different smells. These differences can be felt by the nose.Shapes of small molecules can be bent, pyramidal, tetrahedral, planar, trigonal, etc. Shapes of large molecules can be zigzag, ring, ball or pan shaped.

A space- filling model can predict camphor, minty and sweet smells. Camphor smelling compounds have ball shaped molecules while compounds with mint smell are frying pan shaped. Long and stringy molecules of geraniol smell sweet.

Explanation of Solution

The overall shape of the molecule can be revealed by the three dimensional structure of the molecule. The molecular shape is an accurate predictor of many smells. In some molecules, the carbon atoms are linked in a long chain while in some they contain ring structures. The presence of bonded and lone pair of electrons affect the shape of a molecule. Shapes of small molecule can be bent, pyramidal, tetrahedral, planar, trigonal, etc. shapes of large molecules is determined by shapes of smaller parts of these molecules. For example, shape of heptanoic acid is a series of overlapping tetrahedral shapes.

Most of the smell molecules are large molecules. A space- filling model can help in knowing the overall shape of these molecules. Space- filling models of geraniol, carvone, fenchol and others have revealed that camphor smelling compounds have ball shaped molecules while compounds with mint smell are frying pan shaped. Long and stringy molecules of geraniol smell sweet.

Conclusion

The shape of a molecule is related to its smell. The three dimensional structure of a molecule tells about the shape of a molecule.