Specify the configuration of the following compounds in `D` or `L` designation.
(a)
Strategy: The sterochemicla descriptor `D` refers to an arrangement about a centre of chirality that is identical to the three-dimensional arrangement in `D-(+)-`glyceraldehyde in which the `OH` group on the chiral centre is on the right in the Fischer projection. Similarly, the other enatiomer of glyceraldehyde, which has `_OH` group on the chiral centre to the left is given `L` configuration. For carbohydrates (polyhdroxy aldehydes or ketones) the focus should be on the last chiral carbon (from the top) while for amino acids the focus should be on the chiral carbon carrying the `NH_(2)` group.

Explanation

(a) `L-`configuraiton as the `-OH`on `C-3` is on the left side.
(b) Convert the wedge and dash formula into Fischer projection.

An even number of switches results in no change in the configuration. Since`-NH_(2)` group is one the left, it is designated `L`configuration.
(c ) `D`-configuration since `-OH`group on `C-3` is on right