enantiomeric excess

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enantiomeric excess

[ə¦nan·tē·ō¦mer·ik ek′ses]
(organic chemistry)
In an asymmetric synthesis, a chemical yield that contains more of the desired enantiomer than other products.
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yield (%) 0 (racemic) 100 [less than or equal to] 2 90 0 20 100 [less than or equal to] 35 80 ~20 60 0 50 100 [less than or equal to] 70 50 ~55 40 ~25 30 0 60 100 [less than or equal to] 80 50 ~65 30 ~25 20 0 70 100 [less than or equal to] 85 50 ~80 30 ~60 20 ~25 10 0 80 100 [less than or equal to] 90 30 ~85 20 ~70 10 0 90 100 [less than or equal to] 95 20 <95 10 80 5 0 [a] E (enantiomeric ratio or selectivity factor) = ln[(1 - C)(1 - ee)]/ln[(1 - C)(1 + ee)] C and ee are the extent of conversion and the enantiomeric excess of the unreacted alcohol, respectively d (%) Table 4.
Here, we sought to study some of the chiral markers present in the fruit fibre samples in order to assess whether the processing (which includes thermal treatment) affects the enantiomeric ratio (ER), that is, with an increase of racemisation of some chiral compounds.
The enantiomeric ratio (R:S) of MDA in plasma was found to decrease initially, reaching a minimum (0.02 [+ or -] 0.03) at 2 h, which was followed by a slow but progressive increase to 1.29 [+ or -] 0.15 at 24 h.
Concomitant with the loss of total thalidomide, the change affecting the enantiomeric ratio would be even greater.
Results: Adulteration of a number of tea tree oil samples was demonstrated either by abnormal enantiomeric ratios and/or the presence of compounds that are not known to occur naturally in tea tree oil.
The enantiomeric ratios were 0.78 and 0.74 for 20ng/mL and 200ng/mL of rac-MDMA, respectively.