Question

27. Effect of Polarity on Solubility: Rank the following in order of increasing solubility in water: a triacylglycerol, a diacylglycerol, and a monoacylglycerol, all containing only palmitic acid.

Answer 1

greater is hydrogen bonding, greater is solubility

increasing order of solubility

triacylglycerol < diacylglycerol < monoacylglycerol

in triacylglycerol R(CO)-O - CH(CH2-O-(CO) R)2,

there is no O-H direct bond which is necessary condition for hydrogen bonding. Thus it has no hydrogen bonding, so least solubility in water

in diacylglycerol R(CO)-O-CH(CH2OH)(CH2-O-(CO)R)

it contains one O-H direct bond, so it has hydrogen bonding, so it is soluble in water.

in monoacylglycerol R(CO)-O-CH(CH2OH)2

there are 2 O-H direct bond, so extent of hydrogen bonding is more, so higher solubility.