Chemistry - STEREO ISOMERISM Question with Solution | TestHub

In these Fischer cross structures the horizontal bonds project towards you and the vertical bonds point away. When the lowest-priority group is on a horizontal bond, the result is inverted.

(a) Priorities : OH (1) $>$ COOH (2) $>$ CH₂OH (3) $>$ H (4). H is horizontal (towards you). Tracing 1 $\to$ 2 $\to$ 3 gives R; inverting : S.

(b) Priorities : OH (1) $>$ CHO (2) $>$ CH₃ (3) $>$ H (4). H is horizontal. Tracing 1 $\to$ 2 $\to$ 3 gives S; inverting : R.

(c) Priorities : Br (1) $>$ COOH (2) $>$ CH₃ (3) $>$ H (4). H is horizontal. Tracing 1 $\to$ 2 $\to$ 3 gives R; inverting : S.

(d) Priorities : Cl (1) $>$ COOH (2) $>$ CH₂OH (3) $>$ H (4). H is horizontal. Tracing 1 $\to$ 2 $\to$ 3 gives R; inverting : S.

Ans. (a) S (b) R (c) S (d) S