Which configuration (R or S) does the bottom asymmetric carbon have for the D series of sugars? Which configuration for the L series?

Verified step by step guidance

Identify the bottom asymmetric carbon in the Fischer projection of the sugar.

Assign priorities to the four substituents attached to the bottom asymmetric carbon based on the Cahn-Ingold-Prelog priority rules.

Orient the molecule so that the lowest priority group is pointing away from you.

Determine the order of the remaining three groups: if the sequence is clockwise, the configuration is R; if counterclockwise, it is S.

For D sugars, the bottom asymmetric carbon typically has the R configuration, while for L sugars, it typically has the S configuration.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chirality and Asymmetric Carbons

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of an asymmetric carbon atom. An asymmetric carbon is a carbon atom bonded to four different groups, leading to two possible configurations, known as enantiomers. Understanding chirality is crucial for determining the R or S configuration of sugars.

Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog (CIP) priority rules are a set of guidelines used to assign priorities to the substituents attached to an asymmetric carbon. According to these rules, the substituents are ranked based on atomic number, with higher atomic numbers receiving higher priority. This ranking is essential for determining whether the configuration is R (rectus, right) or S (sinister, left) when viewing the molecule from a specific orientation.

D and L Configuration in Sugars

The D and L notation in sugars refers to the configuration of the asymmetric carbon farthest from the aldehyde or ketone group. In D sugars, this carbon has the same configuration as D-glyceraldehyde, while in L sugars, it has the opposite configuration. This distinction is important for understanding the stereochemistry of carbohydrates and their biological roles.

Recommended video:

Guided course

06:47

Monosaccharides - D and L Isomerism

Related Practice

Textbook Question

Which of the following compounds are chiral? Draw each compound in its most symmetric conformation, star (*) any asymmetric carbon atoms, and draw any mirror planes. Label any meso compounds. You may use Fischer projections if you prefer.

(e) (R,R)-2,3-dibromobutane

(f)

947

views

Textbook Question

(d) (2R,3S)-2,3-dibromobutane

1907

views

Textbook Question

Which of the following pairs of compounds could be separated by recrystallization or distillation?

a. meso-tartaric acid and (±)-tartaric acid (HOOC—CHOH—CHOH—COOH)

1748