Give the IUPAC name for the following compound.
A)R-4-bromo-1-pentyne
B)S-4-bromo-1-pentyne
C)R-3-bromo-5-pentyne
D)S-3-bromo-5-pentyne

Question

Give the IUPAC name for the following compound. 
A)R-4-bromo-1-pentyne 
B)S-4-bromo-1-pentyne 
C)R-3-bromo-5-pentyne 
D)S-3-bromo-5-pentyne

Quizplus · Accepted Answer

The highest priority functional group is the alkyne, which makes the carbon atoms of the triple bond the priority group for assigning R/S configuration. Counting from left to right, the substituent on the second carbon is a bromo group, and the substituent on the third carbon is a hydrogen atom. The bromo group has higher atomic number than hydrogen, so we assign the lowest priority to the hydrogen atom. The remaining two substituents on carbon 1 are both methyl groups with the same priority, so we compare the atoms attached to the methyls. Carbon 2 is attached to a bromine atom, while carbon 3 is attached to a hydrogen atom. Since the bromine atom has a higher atomic number, the methyl group attached to carbon 2 has higher priority, and the molecule is named as S-4-bromo-1-pentyne.

Give the IUPAC Name for the Following Compound