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MindMap Gallery Chemistry-aldehydes and ketones mind map

Chemistry-aldehydes and ketones mind map

This is a mind map about chemistry - aldehydes and ketones, a compilation of medical organic chemistry knowledge points (aldehydes and ketones). The main content includes physical properties, chemical properties, etc.

Edited at 2023-12-03 09:24:51

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Chemistry-aldehydes and ketones mind map

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Outline

Thinking map of α-substitution and condensation reactions of carbonyl compounds
- 60
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aldehydes, ketones

name

physical properties

boiling point

Higher than alkanes and ethers

The carbonyl group is highly polar

Lower than alcohols with similar molecular weights

No intermolecular hydrogen bonds

State (at room temperature)

Gas: formaldehyde

Liquid: aldehydes and ketones below 12 carbons

Solid: higher aliphatic aldehydes, ketones, aromatic ketones

Solubility

Lower aldehydes and ketones are easily soluble in water

Carbonyl oxygen forms hydrogen bonds with water molecules

Water solubility decreases rapidly as the hydrocarbon group increases

chemical properties

α-H active (substituted)

Electron-withdrawing induction of α-C by carbonyl carbon

aldol condensation

In a dilute alkaline solution, the α-carbon (nucleophile) of one aldehyde molecule adds to the carbonyl carbon of another molecule of aldehyde to form β-hydroxyaldehyde.

β-hydroxyaldehyde easily loses water when heated to form α, β-unsaturated aldehyde

The reaction rate decreases as the relative molecular mass increases

Solution: Warm up

Advantages: Promotes reaction

Disadvantages: It is easy to cause the product to lose water

Aldehydes with more than 7 carbon atoms undergo aldol condensation to only obtain α, β-unsaturated aldehydes.

Keto and enol tautomerism

Nitrogen-containing compounds (especially imides) also have tautomerism

Beta-diketones with α-H exist in keto and enol tautomerism

Influencing factors

Enol structural stability

Depends on the conjugation effect between the carbonyl group and the double bond and the formation of a six-membered chelate ring

The enol form mainly exists in the Z configuration

Conducive to the formation of a six-membered chelate ring through intramolecular hydrogen bonding

Solvent, concentration, temperature, etc.

Example: 2,4-Pentanedione

Typical reactions of methyl ketone may occur

Reacts with hydroxylamine to form oxime

Reacts with phenylhydrazine to form hydrazone

Can be combined with HCN

Has enol properties

Color development with FeCl3 solution

Can make bromine water fade

If the α-carbon is a hydrogen-containing chiral carbon, the asymmetry of α-C disappears after the aldehyde and ketone are converted into the enol form.

Reverse reaction: hydroxyl hydrogen is added to α-C with equal opportunity from both sides, and the chiral carbon is racemized.

Halogenation reaction

Under alkali catalysis, halogens react rapidly with α-H-containing aldehydes and ketones to form α-C completely halogenated products.

Haloform reaction

Reaction range: acetaldehyde, methyl ketone, 2-aldehyde

α-C contains 3 active hydrogens; 2-alcohol is easily oxidized to methyl ketone by NaOX

Reaction conditions: NaOH solution of halogen (commonly used alkaline solution of sodium hypohalite)

First generate α-trihalogenate, and then decompose into trihalomethane (haloform) and carboxylate

Application: Iodoform reaction can be used to identify acetaldehyde, methyl ketone and 2-aldehyde

Vulnerable to nucleophile attack (additional)

liveliness

Aldehydes>ketones

Aliphatic aldehydes and ketones>Aromatic aldehydes and ketones

The carbon-oxygen double bond is highly polar (O-, C)

Typical reaction

Addition with hydrocyanic acid (HCN)

HCN reacts with aldehydes, aliphatic methyl ketones, and cyclic ketones with less than 8 carbon atoms to form cyanohydrins (α-hydroxyalcohols)

HCN has difficulty reacting with aromatic ketones

The carbonyl group is conjugated with the aromatic ring, and the carbonyl carbon is less electropositive.

The steric hindrance of aromatic rings and alkyl groups affects the attack of nucleophiles towards carbonyl groups

Usually requires base catalysis

HCN is a weak acid and difficult to dissociate

Experimental Notes

Generally, NaCN or KCN aqueous solution is mixed with aldehydes and ketones, and then sulfuric acid is added dropwise.

This reaction operation should be carried out in a fume hood

HCN is volatile and highly toxic

application

Preparation of α, β-unsaturated cyanide, β-hydroxylamine, etc. from cyanohydrin

Extend the carbon chain (add one carbon atom)

Addition to alcohol

aldehyde

Conditions: Anhydrous acid (usually dry HCl gas) environment

①Addition of alcohol and aldehyde carbonyl group to form hemiacetal ②Dehydration of alcohol and hemiacetal to form acetal

②The hydroxyl oxygen of hemiacetal contains lone electron pairs and is easy to combine with H and dehydrate.

ketone

Difficult to react with alcohol

Easily reacts with ethylene glycol to form five-membered cyclic ketal

(product) acetal, ketal

Stable to alkali, oxidizing agent and reducing agent

Decomposes into original reactants when encountering dilute acid

Application of protected aldehyde groups (commonly used ethylene glycol) During synthesis, the aldehyde is converted into acetal, and then hydrolyzed to release the aldehyde group after oxidation or other reactions are completed.

Special cases: γ- or δ-hydroxyaldehydes and ketones mainly exist in the form of cyclic hemiacetals and ketones

Prone to spontaneous intramolecular nucleophilic addition

Add to water

Addition to form glycol

Unstable, easy to lose water, and the balance is biased towards the reactants.

Water is weakly nucleophilic

Related to the activity of aldehydes and ketones Formaldehyde is extremely reactive, so it is almost entirely hydrated in aqueous solutions.

Methanol hydrate easily loses water during the separation process, so it cannot be separated.

When the carbonyl group is connected to a strong electron-withdrawing group, a more stable hydrate can be formed.

Carbonyl carbon becomes more electropositive

Addition to Grignard reagent

irreversible reaction

Rδ-attacks the carbonyl carbon, Mgδ X combines with the carbonyl oxygen

The addition product is hydrolyzed to form alcohol

Correspondence between products and raw materials

Formaldehyde…primary alcohol

Other aldehydes…secondary alcohols

Ketone…tertiary alcohol

application

Preparation of alcohols with more carbon atoms and new carbon skeletons

Addition to ammonia derivatives

Common derivatives of ammonia

Hydroxylamine, hydrazine, phenylhydrazine, 2,4-dinitrophenylhydrazine, etc.

Can be used to identify carbonyl compounds (especially aldehydes and ketones), called carbonyl reagents

It can also be used for the separation and purification of aldehydes and ketones.

First-grade ammonia must be used (there are 2 H on N)

Addition first and then dehydration to form N-substituted imine

N-substituted imines are easy to crystallize and purify, and can be hydrolyzed by acid to obtain original aldehydes and ketones.

Addition of carbonyl compounds to primary amines produces Schiff bases (reversible)

oxidation reaction

Aldehydes are easily oxidized, but ketones are difficult to oxidize.

Weak oxidants such as silver ammonia solution (Tollens reagent) can be used to identify aldehydes and ketones.

Fehling's reagent (alkaline solution of copper sulfate and potassium sodium tartrate)

Heat together with fatty aldehyde to produce brick red cuprous oxide

Does not react with aromatic aldehydes

Fehling's reagent can be used to identify aliphatic and aromatic aldehydes.

reduction reaction

reduction products of carbonyl groups

Alcoholic hydroxyl group

Metal catalyst (Pt, Ni), H2 addition

metal hydride

Lithium aluminum hydride (LiAlH4)

Strong reducing ability, can reduce most carbonyl groups

It must be added in anhydrous ether, and then the product is hydrolyzed

LiAlH4 easily decomposes when exposed to water or alcohol

Sodium borohydride (NaBH4)

Weak reducing ability, only reduces aldehydes and ketones

Addition and hydrolysis can be completed quickly and continuously in water or alcohol solution

methylene

Reflux with zinc amalgam and concentrated hydrochloric acid

Heat with hydrazine and KOH in a high boiling point solvent (such as diethylene glycol)