Question

Chloral$\mathbf{\left(}{\mathbf{\text{Cl}}}_{\mathbf{\text{3}}}\mathbf{\text{C-CH=O}}\mathbf{\right)}$forms a monohydrate, chloral hydrate, the sleep-inducing depressant called “knockout drops” in old movies.

(a) Write two possible structures for chloral hydrate, one involving hydrogen bonding and one that is a Lewis adduct.

(b) What spectroscopic method could be used to identify the real structure? Explain

Short answer

(a)The 2 possible structures of chloral hydrate was written above

(b)The spectroscopic method is Infrared spectroscopy to identify the real structure

Step-by-step solution

To write two possible structures for chloral hydrate

(a)

Chloral is reduced chloral hydrate. It originally contains 2 hydroxides. The two forms of chloral hydrate are shown below. The first one is the chloral hydrate interacting with the electronegative chlorine via hydrogen bonding. The second one is the chloral hydrate adduct that does not interact with chlorine formed from the reaction of chloral with water via Lewis acid-base reaction.

Hence the 2 possible structures of chloral hydrate were written above.

To find the spectroscopic method

(b)

The thing that separates the two possible structures of chloral hydrate is the presence of hydrogen bonding of the first structure and the adduct structure. A spectroscopic method that can be used to differentiate the two is Infrared spectroscopy.

Infrared spectroscopy detects the types of bond present in a compound by reading the IR emitted, absorbed, or reflected by the compound. This is helpful in determining functional groups and identifying the compound. In this case, we need to confirm the presence of hydrogen bonding. If there is a presence of hydrogen bonding, then structure one is the real structure of chloral hydrate. If not, then the adduct structure is the real structure of chloral hydrate.

Hence the spectroscopic method is Infrared spectroscopy to identify the real structure.