acetals and hemiacetals

reaction of aldehydes and alcohols

alcohol adds to the carbonyl group which gives a hemiacetal

cyclic hemiacetals

are stable

open chain from an aldehyde functional group in equilibrium with closed chain ring forms (alpha and beta)

glucose at equilibrium

36% alpha

64% beta

>0.02% open-chain

hemiacetals and acetals

hemiacetals are intermediates in the formation of acetals

acetal information

stable enough to be isolated and are in carbohydrates

formed when hemiacetals react further with alcohols

acetals in nature

many sugars and complex carbohydrates are held together by acetal bonds - maltose

hydrolysis

the only chemical reaction of acetals

cleavage

gives a hemiacetal and an alcohol - digestion of a carbohydrate

lactose

a disaccharide which links galactose to glucose via a beta(1-4) linkage to glucose

polysaccharides

have tens, hundreds or thousands of monosaccharides linked together through acetal

starch

storage form of glucose in plants, mixture of 2 kinds of polymers

glycogen

storage form of glucose in animals, stored in liver and muscle tissue

cellulose

allows H bonding within chains, leading to an increase in fibre strength

beta(1-4) bonds

no enzyme in humans to digest this

bacteria have such enzymes and some strains are in cattle stomachs