Chapter U2.9, Problem 7E

Interpretation Introduction

Interpretation:

Evidence to show that the structural formula may not always be useful in predicting smell is to be explained.

Concept introduction:

Structural formula of a molecule is very useful as it gives valuable information such as the functional groups present in the molecule. By knowing the functional groups one can predict the molecular properties of the compound such as smell but this information is not enough to predict the distinct smell of a compound.

Answer to Problem 7E

The three alcohols such as geraniol, menthol and fencholsmell differently even though they have the same functional group(-OH). Geraniol smells like rose, menthol has smell of mint and fenchol smells like pine. Their structural formula only reveals that the functional group is hydroxyl. So it is evident that there is something else besides the functional group which determines the smell of a compound.

For example, isopentylacetate and ethyl butyrate have sweet smell due to presence of ester group but looking at their structural formula one cannot predict their distinct smell. Isopentylacetate has smell of bananas and ethy butyrate has smell of pineapple.

Explanation of Solution

Molecules, such as geraniol (C 10 H 18 O ), menthol (C 10 H 20 O ) and fenchol (C 10 H 18 O ) have same functional group, -OH. Their structural formulas are important but they are not sufficient to predict the distinct smell of each compound. There are many ester molecules which have distinct smell. Their structural formula only tells about the functional group (ester) present in them. For example isopentylacetate and ethyl butyrate have sweet smell due to presence of ester group but looking at their structure one cannot judge their distinct smell. It is the three dimensional structure of the molecule which helps in predicting the correct smell of the compound. Isopentylacetate has smell of bananas and ethylbutyrate has smell of pineapple.

Conclusion

The structural formula of a molecule shows that the molecule is flat with the carbon atoms arranged in line whereas the ball and stick model shows the three dimensional structure of the molecule. This helps in better understanding the shape of the molecule. Differently shaped molecules have different smell even if they have the same functional groups.