But this substitution would invert the molecule's R / S labeling, because the CIP priority of CH2OH is lower than that for CO2H but the CIP priority of CH2SH is higher than that for CO2H. For this reason, the D/L system remains in common use in certain areas of biochemistry, such as amino acid and carbohydrate chemistry, because it is convenient to have the same chiral label for the commonly occurring structures of a given type of structure in higher organisms. In the D/L system, they are nearly all consistent—naturally occurring amino acids are all L, while naturally occurring carbohydrates are nearly all D. In the R / S system, they are mostly S, but there are some common exceptions.