Organic Chemistry

Organic Chemistry - Ch 11 542 Daley & DaleyH HThus, C C becomesCCbecomes C CHHH, and CHCCO becomesHCCH, C C HHC O. Thus, forC CO Cexample, a carbon double bonded to another carbon is considered asthough it was bonded to two carbonsAfter you have determined the priority of the groups label thegroup with the highest priority atom 1. The group with the nexthighest priority label 2, the group with the third highest priority label3, and the group with the lowest priority label 4.Finally, draw the molecule with the lowest priority group backand the other three groups in front of the plane of the paper.21C34When the molecule is drawn with this orientation, add a curved arrowpointing from number 1, past number 2, and on to number 3.21C34If the curved arrow is clockwise, the isomer drawn is the (R) isomer. Ifthe arrow curves counterclockwise the isomer is the (S) isomer.The amino acid serine has one stereocenter with —NH 2 , —CH 2 OH, —COOH, and —H bonded to it. The highest priority group isthe —NH 2 group because nitrogen has the highest atomic number.The carboxylic acid comes next because it has two oxygens, with one ofthem doubly bonded to carbon. The —CH 2 OH is third with only oneoxygen. Last is the hydrogen because it has the lowest atomic number.The figure below shows the two enantiomers of serine, the naturallyoccurring serine on the left and the synthesized serine on the right.The structure of the naturally occurring serine molecule is (S); thestructure of the synthesized serine is (R).www.ochem4free.com 5 July 2005