When determining the absolute R/S configuration from a standard 2D Fischer projection, what immediat — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

In a Fischer projection, horizontal lines represent bonds projecting out towards the viewer. If the lowest priority group is on a horizontal bond, the standard viewing perspective is violated. The rule dictates tracing the $1 \rightarrow 2 \rightarrow 3$ path and then reversing the result (R to S, or S to R) to obtain the true absolute configuration.