Question

1. What easily identified type of vibration(s) (give functional group and approximate expected frequency) would be present in the IR spectrum of the isobutyraldehyde reactant but not in the product 2-methyl-3-heptanol, allowing the compounds to be distinguished?

2. What easily identified type of vibration(s) (give functional group approximate expected frequency) would be present in the IR spectrum of 2-methyl-3-heptanol but not in either of the reactants, allowing the compounds to be distinguished?

3. Does the IR spectrum of the example student sample show product and, if so, is it relatively pure (how conclusive is the spectrum? does it show the product peak identified in question 2 above and/or the reactant peak identified in question 1 above?)

4. identify how many peaks are expected in the ¹³C-NMR for the 2-methyl-3-heptanol product and explain your reasoning, ie. identify mirror planes or rotations that exchange equivalent carbons.

Answer 1

1. As isobutyraldehyde is an adlehyde having carbonyl (C=O) stretching vibrations frequency at around 1700 cm^-1 which is absent in the product 2-methyl-3-heptanol. The product is an alcohol which has O-H stretching frequency between 3300-3500 cm^-1 which is absent in the product. So, these easily identified type of vibration(s) allow the compounds to be distinguished.

2. One of the reactants is isobutyraldehyde which is an aldehyde and the other one is butyl bromide which is a bromoalkane. The product is 2-methyl-3-heptanol and has hydroxyl group which is absent in both of the reactants. The O-H stretching frequency is observed between 3300-3500 cm^-1.

So, O-H stretching frequency observed in the 3300-3500 cm^-1 is easily identified type of vibration is present in the IR spectrum of 2-methyl-3-heptanol but not in either of the reactants, allowing the compounds to be distinguished

3. The IR spectrum of the example student sample show product, its purity should be known by matching of the mentioned frequencies in the spectrum of the samples.

4. The number of peaks expected in the ¹³C-NMR for the 2-methyl-3-heptanol product = number of magnetically non equivalent carbon atoms = 7

So, the number of peaks expected in the ¹³C-NMR for the 2-methyl-3-heptanol product is seven.

The mirror planes or rotations that exchange equivalent carbons (1) are the ones passing between the carbon atoms 2 and 3.