last lab quiz Flashcards
X-Mg-Br is nucleophilic why?
separation of charge: Mg+ R-
grignards and ketones, aldehydes
Adds R (once) and reduces to OH
Role of crushing Mg
activation by removing oxidation. iodine can activate it, too.
grignards in protic solvents
act like bases
Vinyl halides, terminal alkyne halides
can be grignard reagents!
Alcohols present, acidic protons, F, or no halogen
Can’t be grignard agents
Why keep water out?
Grignard loves nonpolar aprotic solvents. dilute with ether to prevent dimerization (but too much inhibits product formation)
why ethers?
Have Lewis basic lone pairs, help solvate Mg cation. polar solvents sequester partial charges, making rxn less likely.
what does workup do?
takes off the mgbr from alkoxide intermediate.
starting with ester, amide, thioester
adds R twice (2 equivalents) no matter what! If you don’t have enough grignard, you’ll get half double additions and half starting material
epoxides
basically a carbonyl. more electrophilic than ester. adds least hindered.
Which face? Grignard.
Less hindered.
grignard adds only once to acid chloride. why?
one add forms ketone=less reactive species.
CO2 + Gringard
Carboxylic acid.
ylide resonance
- charge on carbon, attacks carbonyl in mechanism
