An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. (Where -R represents the carbon chain.) ==Structure== The aldehyde functional group is a carbonyl group bonded to a hydrogen atom and a carbon atom. ===α carbon & α hydrogen=== An α (alpha) carbon is a carbon adjacent to a carbonyl group. An α hydrogen is a hydrogen atom bonded to the α carbon. The pKa of an α hydrogen is 20. ===Carbonyl group=== The other molecules containing a carbonyl group are: *Ketones *Carboxylic acids ==Nomenclature== Aldehydes are named by IUPAC nomenclature by changing the suffix ''-e'' of the parent alkane to ''-al''. Aliphatic aldehydes are named as derivatives of their longest alkyl chain. Thus, HCHO is named as a derivative of methane, and CH3CH2CH2CHO is named as a derivative of butane. The suffix -al replaces the -e of the alkane name. Thus, HCHO is named methanal, more commonly known as formaldehyde, and CH3CH2CH2CHO is named butanal. When a -CHO group is attached to a ring, the suffix -carbaldehyde is used. Thus, C6H11-CHO is known as cyclohexanecarbaldehyde. The name benzaldehyde is used as the root for aldehydes derived from benzene. ==Physical properties== The carbonyl group is polar molecule. ==Chemistry== ===Preparation=== There are three notable methods for preparing aldehydes: * Reacting a Alcohol#Primary.2C_Secondary.2C_and_Tertiary_Alcohols with an oxidizing agent, * Reacting an alkene (if there is a vinylic hydrogen) with ozone will cause the C=C bond to break yielding an aldehyde upon workup, in a process called ozonolysis. * Reacting an ester with DIBAL-H can cause reduction, yielding an aldehyde. The primary means of synthesis is the oxidation of a primary alcohol. In the laboratory this may be achieved by heating the alcohol with a chromium(VI) reagent an acidified solution of potassium dichromate, which is redox to green Cr3+ during the reaction. Excess dichromate will further oxidise the aldehyde to form a carboxylic acid, so either the aldehyde is distillation out as it forms (if Vapor_pressure), or milder methods such as pyridinium chlorochromate oxidation or Swern oxidation are used. The equation is shown below with propan-1-ol being oxidised to form propanal. CH3CH2CH2OH —→ CH3CH2CHO A similar process reacting pentan-1-ol to form pentanal is illustrated below. ===Common reactions=== *aldehyde + alcohol + acid or base (chemistry) —→ hemiacetal *hemiacetal + alcohol + acid catalyst —→ acetal + water :Simple hemiacetals are usually unstable, although cyclic ones such as glucose do exist. Acetals are stable, but these revert to the aldehyde in the presence of aqueous acid. * Treating aldehydes with oxidizing agents such as potassium permanganate, nitric acid, or chromium(VI) oxide, will yield a carboxylic acid. * Treating aldehydes with Tollens' reagent (which is prepared by adding a drop of sodium hydroxide solution into silver nitrate solution to give a precipitate of silver(I) oxide, and then adding just enough dilute ammonia solution to redissolve the precipitate in aqueous ammonia to produce [Ag(NH3)2]+ complex) will convert aldehydes to carboxylic acids without attacking carbon-carbon double bonds. See also [http://www.wiu.edu/users/mftkv/Chemistry102/oxidationaldehydes.html oxidation of aldehyde] * Aldehydes can react with water (under acidic or basic conditions) to form hydrate, R-C(H)(OH)(OH), although these are only stable when strong electron withdrawing groups are present as in chloral hydrate. The mechanism is identical to hemiacetal formation. * Aldehydes can react with Hydrogen cyanide to form cyanohydrins, R-C(H)(OH)(CN). * Treating an aldehyde with a Grignard reagent can yield an alcohol with a substituted group from the Grignard reagent. * Treating aldehydes with hydrazine will reduce a C=O bond to CH2 via the Wolff-Kishner reaction. ===Nucleophilic addition=== #aldehyde + nucleophile —→ tetrahedral carbonyl addition compound #*aldehyde + ammonia or primary amine —→ tetrahedral carbonyl addition compound #**tetrahedral carbonyl addition compound + acid (catalyst) —→ imine + water (molecule) ===Keto-enol tautomerism=== Equilibration of keto and enol tautomers is catalyzed by acid. ===Oxidation & Reduction=== *Aldehydes are oxidized to carboxylic acids. *Aldehydes are reduced to primary alcohols. ==Examples of Aldehydes== * Methanal (Formaldehyde) * Ethanal (Acetaldehyde) * Propanal * Butanal * Pentanal * Glucose ==See also== *Ketone Aldehydes su:aldehida
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Words begining with Aldehyde:
Aldehyde
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Aldehydes
Aldehyde
An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. (Where -R represents the carbon chain.) ==Structure== The aldehyde functional group is a carbonyl group bonded to a hydrogen atom and a carbon atom. ===α carbon & α hydrogen=== An α (alpha) carbon is a carbon adjacent to a carbonyl group. An α hydrogen is a hydrogen atom bonded to the α carbon. The pKa of an α hydrogen is 20. ===Carbonyl group=== The other molecules containing a carbonyl group are: *Ketones *Carboxylic acids ==Nomenclature== Aldehydes are named by IUPAC nomenclature by changing the suffix ''-e'' of the parent alkane to ''-al''. Aliphatic aldehydes are named as derivatives of their longest alkyl chain. Thus, HCHO is named as a derivative of methane, and CH3CH2CH2CHO is named as a derivative of butane. The suffix -al replaces the -e of the alkane name. Thus, HCHO is named methanal, more commonly known as formaldehyde, and CH3CH2CH2CHO is named butanal. When a -CHO group is attached to a ring, the suffix -carbaldehyde is used. Thus, C6H11-CHO is known as cyclohexanecarbaldehyde. The name benzaldehyde is used as the root for aldehydes derived from benzene. ==Physical properties== The carbonyl group is polar molecule. ==Chemistry== ===Preparation=== There are three notable methods for preparing aldehydes: * Reacting a Alcohol#Primary.2C_Secondary.2C_and_Tertiary_Alcohols with an oxidizing agent, * Reacting an alkene (if there is a vinylic hydrogen) with ozone will cause the C=C bond to break yielding an aldehyde upon workup, in a process called ozonolysis. * Reacting an ester with DIBAL-H can cause reduction, yielding an aldehyde. The primary means of synthesis is the oxidation of a primary alcohol. In the laboratory this may be achieved by heating the alcohol with a chromium(VI) reagent an acidified solution of potassium dichromate, which is redox to green Cr3+ during the reaction. Excess dichromate will further oxidise the aldehyde to form a carboxylic acid, so either the aldehyde is distillation out as it forms (if Vapor_pressure), or milder methods such as pyridinium chlorochromate oxidation or Swern oxidation are used. The equation is shown below with propan-1-ol being oxidised to form propanal. CH3CH2CH2OH —→ CH3CH2CHO A similar process reacting pentan-1-ol to form pentanal is illustrated below. ===Common reactions=== *aldehyde + alcohol + acid or base (chemistry) —→ hemiacetal *hemiacetal + alcohol + acid catalyst —→ acetal + water :Simple hemiacetals are usually unstable, although cyclic ones such as glucose do exist. Acetals are stable, but these revert to the aldehyde in the presence of aqueous acid. * Treating aldehydes with oxidizing agents such as potassium permanganate, nitric acid, or chromium(VI) oxide, will yield a carboxylic acid. * Treating aldehydes with Tollens' reagent (which is prepared by adding a drop of sodium hydroxide solution into silver nitrate solution to give a precipitate of silver(I) oxide, and then adding just enough dilute ammonia solution to redissolve the precipitate in aqueous ammonia to produce [Ag(NH3)2]+ complex) will convert aldehydes to carboxylic acids without attacking carbon-carbon double bonds. See also [http://www.wiu.edu/users/mftkv/Chemistry102/oxidationaldehydes.html oxidation of aldehyde] * Aldehydes can react with water (under acidic or basic conditions) to form hydrate, R-C(H)(OH)(OH), although these are only stable when strong electron withdrawing groups are present as in chloral hydrate. The mechanism is identical to hemiacetal formation. * Aldehydes can react with Hydrogen cyanide to form cyanohydrins, R-C(H)(OH)(CN). * Treating an aldehyde with a Grignard reagent can yield an alcohol with a substituted group from the Grignard reagent. * Treating aldehydes with hydrazine will reduce a C=O bond to CH2 via the Wolff-Kishner reaction. ===Nucleophilic addition=== #aldehyde + nucleophile —→ tetrahedral carbonyl addition compound #*aldehyde + ammonia or primary amine —→ tetrahedral carbonyl addition compound #**tetrahedral carbonyl addition compound + acid (catalyst) —→ imine + water (molecule) ===Keto-enol tautomerism=== Equilibration of keto and enol tautomers is catalyzed by acid. ===Oxidation & Reduction=== *Aldehydes are oxidized to carboxylic acids. *Aldehydes are reduced to primary alcohols. ==Examples of Aldehydes== * Methanal (Formaldehyde) * Ethanal (Acetaldehyde) * Propanal * Butanal * Pentanal * Glucose ==See also== *Ketone Aldehydes su:aldehida
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AB | AC | AD | AE | AF | AG | AH | AI | AJ | AK | AL | AM | AN | AO | AP | AR | AS | AT | AU | AW | AX | AY | AZ |Words begining with Aldehyde:
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