MCAT Organic Chemistry - Alcohols

269

hydroxyl group (alcohols)

-OH

are capable of intermolecular hydrogen bonding → significantly higher melting and boiling points (additive) + solubility in water

• IUPAC: root alkane - -e + -ol

• common: alkyl group + alcohol

  • not highest priority: hydroxy-

phenols

hydroxyl groups attached to aromatic rings; particularly acidic due to resonance within the phenol ring

two substituents - indicate relative positions

ortho–/o–

Two groups on adjacent carbons on a benzene

meta–/m–

Two groups separated by a carbon on a benzene

para–/p–

Two groups on opposite sides of the ring

hydrogen bond

the partially positive hydrogen of one molecule electrostatically attracts the partially negative oxygen of another molecule, generating a noncovalent bonding force

acidity of alcohols

hydroxyl hydrogen is weakly acidic; can dissociate into protons and alkoxide ions in the same way that water dissociates; electron-withdrawing substituents increase acidity, and electron-donating groups decrease acidity

pyridinium chlorochromate (PCC)

mild anhydrous oxidant

oxidises primary alcohols to aldehydes; does not continue

Secondary alcohols can be oxidized to ketones

geminal diols (1,1-diols)

other oxidizing agents (not PCC) oxidise aldehydes, which can be easily oxidized to carboxylic acids

ex. sodium and potassium dichromate salts (Na2Cr2O7 and K2Cr2O7)

Tertiary alcohols

cannot be oxidized because they are already as oxidized as they can be without breaking a carbon–carbon bond

Jones oxidation

chromium trioxide, CrO3, dilute sulfuric acid, H2SO4, in acetone; oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones

mesylate

−SO3CH3

derived from methanesulfonic acid

made from methylsulfonyl chloride and an alcohol in the presence of a base

good leaving group, good protecting group

Tosylates

−SO3C6H4CH3

derived from toluenesulfonic acid

are produced by the reaction of alcohols with p-toluenesulfonyl chloride, forming esters of toluenesulfonic acid

good leaving group, good protecting group

acetals

primary carbons with two −OR groups and a hydrogen atom

ketals

secondary carbons with two −OR groups

deprotection

acetal or ketal can be reverted back to a carbonyl with aqueous acid

protection

save a ketone/aldehyde from reacting by reacting with diol then deprotecting

quinones (2,5-cyclohexadiene-1,4-diones)

treatment of phenols with oxidizing agents; resonance-stabilized electrophiles but not necessarily aromatic; electron acceptors biochemically

number carbonyl position + quinone

ex. vutamins K1, K2

Vitamin K1 (phylloquinone)

2-methyl-3-[(2E)-3,7,11,15-tetramethylhexadec-2-en-1-yl]naphthoquinone

important for photosynthesis and the carboxylation of some of the clotting factors in blood

fat-soluble vitamins that play a role in carboxylation of clotting factors II, VII, IX, and X, and proteins C and S in blood

Vitamin K2 (menaquinones)

protective effect on bone mineral density and reduced risk of hip, vertebral and non-vertebral fractures

fat-soluble vitamins that play a role in carboxylation of clotting factors II, VII, IX, and X, and proteins C and S in blood

Hydroxyquinones

quinones with one or more hydroxyl groups; behave like quinones with electron-donating groups - slightly less electrophilic

ex. Tetrahydroxybenzoquinone; 5-hydroxynaphthoquinone; 1,2-dihydroxyanthraquinone.

hydroquinone

benzene ring with two hydroxyl groups

Ubiquinone/coenzyme Q

biologically active quinone; vital electron carrier associated with Complexes I, II, and III of the electron transport chain

reduced to ubiquinol upon the acceptance of electrons