OChem 5:Carbonyls and Alcohols (comp) Flashcards

Terms Definitions
Basic physical properties of alcohols.
Polar, hydrophilic molecules. Increase in molecular mass increase boiling point while branching decreases it.
Why are alcohols no ideal nucleophiles?
The alkoxide anion is very basic, this strong basicity makes it a bad Nu because it will often depronate and cause elimination.
IR for aldehydes and ketones
1710 cm⁻¹ to 1740 cm⁻¹ range.
The C-H stretches is at 2700 cm⁻¹ to 2900 cm⁻¹ range for aldehydes.
NMR for aldehydes.
The H can be found at 9 and 10 ppm.
What are conditions for the making and removing hemi acetals/ketals and acetals/ketals?
Acetals and metals are formed and removed only under acidic condition.
Hemi-acetal/ketals are formed only under basic condition but can be removed in any condition.
Mechanism for formation of metals under acidic condition.
Mechanism formation of hemiacetals basic condition.
pKa value for carboxylic acids.
pka between 2 and 5 so they are weak acids.
Define reactivity of esters.
They have a leaving alkoxy group. The reactivity correlates with the pKa value of the leaving group. The more stable the leaving group means a lower pKa value making it less basic.
What are acid anhydrides?
Formed by a condensation reaction of two carboxylic acids at high temp.
What are the three types of reactions carbonyls can have?
1. An electrophile attack the nucleophile carbonyl carbon to make a tetrahedral intermediate.
2. Deprotonation of the alpha proton to make an anion such as in adol reactions.
3. Oxidation/reduction reactions.
List the reactivity of leaving groups from best to worse.
The more stable (less basic) the leaving group the better the leaving group.
If the leaving group is too basic, it will become the nucleophile.
Basic mechanism for nucleophile attack of carbonyls.
Basic mechanism for formation of enolate anion.
The alpha proton is a weak acid, so a strong base is needed to strip it from the alpha carbon.
Mechanism for the formation of enolate to extend a ketone.
What is the kinetic enolate?
At low temperature with a bulky base, the less
hindered (less substituted) alpha carbon gets deprotonated to form the so called kinetic enolate (lower energy transition state).
What is the thermodynamic enolate?
At a higher temperature with a small base, the more hindered (more substituted) alpha carbon gets deprotonated to form the so called thermodynamic enolate (leading to the more stable product).
Ketone react with C₆H₅CO₃H (peroxybenzoic acid)
Alcohol react with KMnO₄
What is LAH more reactive than NaBH₄?
The two most common reducing agents in carbonyl chemistry are LAH and NaBH₄. Aluminum is less electronegative than boron, so LiAlH₄ is more apt to donate an H⁻ to the carbonyl carbon, and thus is more reactive than NaBH₄.
What are the limitations of NaBH₄?
The only carbonyl compound it reduce is aldehyde and ketones
Mechanism for Grignard reaction with a leaving group.
Rules of Grignard reacting with epoxides.
It will act the side that is less sterically hindering. This is a Sn2 like mechanism.
Gilman reagent
Aldol Mechanism
Aldol reaction with a Nitro group to add a nitrogen.
Intramolecular aldol reaction of 2,7-octanedione.
Typical a 5 or 6 carbon ring is formed because they are the most stable ring structures.
Claisen Condensation meachanism
It produces a β-ketoester.
What type of base is require for Claisen?
A base should be similar to the leaving group so that transesterification does not occur. If a strong base is used such as NaOH, the ester will be hydrolyze the ester instead.
Transesterfication mechanism.
Fischer Esterfication
Wittig Reaction mechanism.
Iodoform reaction.
Reacts with methyl ketones only and converts it to a carboxylic acid.
Clemmenson Reaction
It reduces the carbonyl carbon of aldehyde or ketones to alkanes.
It used concentrated HCl so it can't be used if there is an acid sensitive group
Wolf-Kischner Reaction
It reduces the carbonyl carbon of aldehyde or ketones to alkanes. Uses hydrazine
Wolf-Kischner Mechanism
What is used to protect alcohols in synthetic reactions?
Silyl ethers
The carboxylic acid needs to have a β carbonyl carbon.
This allows it to form a stable 6 ring transition state.
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