hydrate, hemiacetals, and acetals

hydrate

geminal diol, contains two OH groups

acidic reaction conditions

positive or neutral intermediates only, strongest acid is H3O, strongest base is water

basic reaction conditions

negative or neutral intermediates only, strongest acid is water, strongest base is OH

how will carbonyls form hydrates under acidic conditions?

H3O will protonate O forming a pos charge, water will attack C at double bond and break to remove pos charge, another molecule of water will deprotonate remaining positive oxygen

how will carbonyls form hydrates under basic conditions?

OH will attach C at carbonyl, breaking double bond forming neg O, water will protonate neg O

hemiacetal and hemiketal

carbonyl analog with one OH and one OR group

when do cyclic hemiketals form?

when the solvent used leads to equilibrium being favored in the cyclic form

H+/2 eq R-OH

acetal formation from an aldehyde or ketone using R group from alcohol, 8 step mechanism with hemiacetal being formed at the 4th step

what are the usual alcohols being used to form acetals?

pTsOH, strong acid and soluble in organic compounds

what condition can acetals not be formed under?

basic or neutral

p-TsOH/diol

aldehyde or ketone to cyclic acetal (double bond split to form ring)

how do you revert cyclic acetals back to carbonyls?

hydrolysis (H3O)

what is the best synthetic use for cyclic acetal formation?

to create a protecting group for OH molecules in organometallic reactions

p-TsOH/ 2 eq R-SH

aldehyde or ketone to diothioacetals

BF3/dithiol

aldehyde or ketone to cyclic dithioacetals

H2/Raney Ni

dithioacetal to alkane, will also reduce alkenes and alkynes

carbonyl to alkane

form dithioacetal from carbonyl and reduce with Raney nickel