introduction to reactions Flashcards
(10 cards)
What is Hammonds postulate?
if 2 states e.g. transition state and an unstable intermediate occur consecutively during a reaction process and have nearly the same energy content, their interconversion will involve only a small reorganisation of the molecular structure.
What does anti-periplanar mean?
In order for a reaction to begin, the C-H and C-Y bond orbitals must overlap, where the H and Y groups are on opposite sides of the central C-C bond. It can be crucial for certain reactions like E2 elimination.
What is grignard addition?
The addition of a grignard reagant (contains a C-Mg bond) to a ketone or aldehyde. Add the Grignards reagant first and then acid.
To consider:
1. This reaction makes a new C–C bond.
2. Many different Grignard reagents can be formed, with R being a simple alkyl group, or a more complex functionalized alkyl group (if you can make the alkyl halide, you can generally make the Grignard reagent!) or aryl (a benzene ring or similar).
3. The reaction produces an alcohol which can be used in subsequent reactions
Describe ester hydrolysis, under acidic conditions
If you dissolve an ester in water and an acid, the ester will be hydrolysed. If you dissolve a carboxylic acid in an alcohol solvent and add an acid, an ester will be made.
Describe ester hydrolysis, under basic conditions
The hydroxide anion is the conjugate base of water, the alkoxide anion in the conjugate base of an alcohol.
The hydroxide ion (OH-) attacks the electrophilic carbonyl carbon of the ester, forming an intermediate. The carbonyl bond reforms, and the alkoxide group (ROR) is eliminated, forming a carboxylic acid. The alkoxide then deprotonates the carboxylic acid, forming a carboxylate salt and an alcohol.
Can use an organic solvent for under basic conditions and make it irreversible
Describe ester formation
from carboxylic acids and alcohols through formal dehydration (loss of h2o)
Describe amide formation.
Amides are formally made by dehydration of a carboxylic acid and an amine. Amine is the nucleophile.
Amides can also be formed by reacting an acyl chloride with an amine. (this can also be done with acid anhydrides)
Describe amide hydrolysis.
Basic conditions don’t work, so its under acidic conditions.
The carbonyl on the amide is protonated, the water attacks the carbonyl C, then proton transfer occurs to give a neutral nitrogen leaving group (like NH4+) leaving a carboxylic acid
Why don’t we add a nucleophile to a C=C?
A primary carbanion is produced, they are unstable and would just collapse. It is possible to add a nucleophile to C=C indirectly on bigger molecules, (on enolate for example) by putting the -ve charge to the oxygen and then shifting the double bond, as O- is stable.
Which position is favoured? Ortho, meta or para?
on toluene
With para, if the electrophile is too big then the stereochemistry with CH3 wont work. Ignoring the steric effect, the ratio of ortho:para is 2:1, this is because there are twice as many ortho positions.
If the ratio turns out to be 1:1 then there is a steric factor (the electrophile might be too big)
