Figure 5.12. Oxidation of p-Benzenediol (a Hydroquinone) to a QuinoneQuinones are named by indicating the position of the carbonyls numerically and adding quinone to
the name of the parent phenol. Due to the conjugated ring system, these molecules are resonance-
stabilized electrophiles. Remember, however, that these are not necessarily aromatic because they
lack the classic aromatic conjugated ring structure. Some quinones do have an aromatic ring, but
this is not always the case. Quinones serve as electron acceptors biochemically, specifically in the
electron transport chain in both photosynthesis and aerobic respiration. Vitamin K 1 is the common
name of the quinone 2-methyl-3-[(2E)-3,7,11,15-tetramethylhexadec-2-en-1-yl]naphthoquinone,
shown in Figure 5.13. This molecule is also called phylloquinone and is important for
photosynthesis and the carboxylation of some of the clotting factors in blood. Vitamin K 2 , similarly,
corresponds to a class of molecules called menaquinones.
Figure 5.13. Phylloquinone (Vitamin K 1 )BRIDGE
Phylloquinone and menaquinone are the common names of Vitamin K 1 and Vitamin K 2 ,
respectively. These molecules are fat-soluble vitamins that play a role in carboxylation of
clotting factors II, VII, IX, and X, and proteins C and S in blood. The functions of fat-soluble
vitamins are explored in Chapter 5 of MCAT Biochemistry Review.