In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. Because the two isomers rotate plane-polarised light (they are optically active) in opposite directions, a racemic mixture does not rotate plane-polarised light. The first known racemic mixture was 'racemic acid', which Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid. Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ... In chemistry, a molecule is chiral if it is not superimposable on its mirror image regardless of how it is contorted. ... This article treats polarization in electrodynamics. ... When polarized light is passed through a substance containing chiral molecules (or nonchiral molecules arranged asymmetrically), the direction of polarization can be changed. ... Racemic acid is an optically inactive form of tartaric acid. ... Louis Pasteur (December 27, 1822 – September 28, 1895) was a French microbiologist and chemist who demonstrated the germ theory of disease and developed techniques of inoculation, most notably the first vaccine against rabies. ... Tartaric acid is a white crystalline organic acid. ...
There are three types of racemates - racemic modifications:
Racemic mixture or better racemic conglomerate
It's the mechanical mixture of enantiomerically pure crystals of one enantiomer and its opposite. Molecules (in the crystal structure) have higner affinity to the same enantiomer, than to the opposite enantiomer. The melting point of the racemic conglomerate is always lower than the pure enantiomer. By addition of small amount of one enantiomer to the racemic compound, the melting point increases.
Racemic compound or just racemate
Molecules have higner affinity to the opposite enantiomer, than to the same enantiomer. By addition of small amount of one enantiomer to the racemic compound, the melting point decreases. But the pure enantiomer can have higher or lower melting point than the racemic compound.
Racemic solid solution or pseudoracemate
Unlike the racemic compound or conglomerate, there is no big difference in affinity between the same and opposite enantiomers. By addition of small amount of one enantiomer to the racemic compound, the melting point changes just little bit, or not at all.
The reagents of, and the reactions that produce, racemic mixtures are said to be "not stereospecific" or "not stereoselective", for their indecision in a particular stereoisomerism. The melting point of a solid is the temperature at which it changes state from solid to liquid. ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ...
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis.
In a raceme, the oldest flowers are borne towards the base and new flowers are produced as the shoot grows.
Raceme (spray) yield was recorded weekly for K706-18 progenies from July 1990 until December 1993, while progenies of the other three amphidiploids were observed from June 1993 to June 1996.
Scape length was measured from the point of attachment to the pseudobulbs to the lowest flower, while raceme length was measured from the point of attachment to the pseudobulbs to the tip of the raceme.
Mean raceme yield per plant from July 1990 to December 1993, scape length, raceme length, and number of flowers per raceme of K706-18 progenies.
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