Are there any chiral molecules that react with their opposites?

Question

Total layman's question just out of pure curiosity. Are there any examples of a chiral molecule where a reaction takes place when two mirrored molecules interact? Or are these interactions always inert?

Answer 1

This is an interesting question and a brief search [unaided by AI] gave no clues. I am assuming you mean: 'Can an enantiomer react with its enantiomer in the same manner as it reacts with itself?'. An example: two + or two -Glucose molecules combine to give a maltose molecule [++ or --]. Can a +glucose and a -glucose react to give a "maltose" molecule with the exact same linkage [+- or -+]. A search finds nothing; perhaps a knowledgeable sugar chemist has info.

There is some information. I have been intrigued by the properties of tartaric acid. Data from 2 editions of Lange's handbook and Wikipedia [very similar probably the same source] give different properties for the enantiomers and the racemic mixture: MP + or - 169C, racemate 205C; solubility in water + or - 1.3KgL racemate 0.2Kg/L. The racemate seems to be of lower energy than optically active. It is also interesting that the natural source seems to be the + isomer but the compound racemizes in fermentation and heating suggesting the racemate is of lower energy; again various sources conflict in this observation. The lower energy suggests there is a stronger interaction between + and - than between + and +, possibly a dimerization.

A possible way to study this is to construct models and study the physical interactions.

Answer 2

You can answer this question in two steps:

1. Are there examples of identical molecules reacting with another?
2. Does is matter if mirror-image molecules are attach to those?

For the first question, the answer is yes. Two aldehydes react in an aldol condensation (identical or not). Two terminal alkenes react with each other in olefin condensation. You can also think of head-to-tail reactions, with two amino acids forming a peptide bond.

For the second question, I don't have a literature example, but imagine putting a long linker on the two molecules and attaching a chiral marker at the end (D or L alanine, say). There is not reason to suspect that the reaction at the other end of the linker would be influenced by whether the two chiral markers match or don't match.

Depending on the nature of the reaction, you would obtain up to four different products (there is no way of preventing identical molecules reacting with each other as you try to react those of opposite chirality with each other).

While I don't know how they synthesized it, D-Alanyl-L-alanine is available for purchase (this does not answer the question, though): https://www.targetmol.com/compound/D-Alanyl-L-alanine