Carbonyl group is composed ofcarbonandoxygentwo typesatomOrganic functional groups connected by double bonds (C=O)[1], Yesaldehyde, ketonecarboxylic acid, carboxylic acid derivatives and other functional groups.In organic reactions, carbonyl can occurNucleophilic addition reaction, reduction reaction, etc. The carbonyl group of aldehyde or ketone can also undergo oxidation reaction.In addition, in coordination chemistry, carbon monoxide ligands are also called carbonyls.
The carbonyl group is generally defined astwoOr sp hybrid carbon atom and an oxygen atom through double bondGroup。
In organic chemistry,Carbonyl compoundIt refers to a class of compounds containing carbonyl groups.
The other two bonds of the carbon atom constituting the carbonyl group can be combined with other atoms or groups in the form of single bond or double bond to form a wide range of carbonyl compounds.
Carbonyl compounds can be divided into aldehyde ketones and carboxylic acids (R is alkyl)
Aldehydes and ketones both contain a common functional group - carbonyl, so they are collectively calledCarbonyl compound。In aldehyde molecules, the carbonyl group must be directly connected with at least one hydrogen atom, so the aldehyde group must be located at the end of the chain.[2]
Naming of common carbonyl compounds:
(1) Common nomenclature
Aldehydes are named after the carboxylic acids formed after oxidation, and ketones are regarded as derivatives of ketones.
availableα、β、γ、δEqual mark substituent position.
(2) System nomenclature
When the molecule contains multiple functional groups, first determine a main functional group, and then select the longest carbon chain containing the main functional group and as many functional groups as possible as the main chain.The principle of numbering the main chain is to make the position of the main officer team as small as possible.When naming, determine the name of the parent body according to the main functional group. Other functional groups are represented by prefixes as substituents. If three-dimensional structures are involved in molecules, indicate their configuration at the front of the name, and then write the name according to the basic format of the name.
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Material structure
The double bond of carbonyl C=O has a bond length of about 1.22 angstroms.Because of oxygenElectronegativity(3.5) Greater than the electronegativity of carbon (2.5), C=O bondElectronic cloudThe distribution is biased towards oxygen atoms: this characteristic determines thePolarityAnd active chemical reactivity.
Bonding modes in clusters
In carbonyl groupCluster chemistryCarbonyl ligands have many different bonding modes.Most common carbonyl ligands are terminal ligands, but carbonyl groups also often connect two or three metal atoms to form μtwoOr μthreeThe bridging ligand of.Sometimes the carbon andOxygen atomWill participate in bonding, such as μthree-η is aHaptoe numberIs 2, a bridging ligand connecting three metal atoms.Metal central atom formationFeedback π bondThe M-C bond energy is enhanced and the C-O bond is activated.[2]
physical property
Boiling point: The carbonyl group has a dipole moment, which increases the attraction between molecules. The boiling point is higher than that of alkanes with corresponding molecular weight, but lower than that of alcohols.
Water solubility: oxygen atoms of aldehydes and ketones can form with waterhydrogen bondTherefore, low-grade aldehydes and ketones can be miscible with water.[2]
The infrared spectrum of carbonyl group has a very strong stretching vibration absorption peak between 1750~1680 cm ⁻ ¹. We call this frequency range the characteristic frequency of carbonyl group. The stretching vibration absorption position of carbonyl group in different carbonyl compounds is slightly different[3]。
Infrared characteristics of carbonyl complexes
In the analysis of metal carbonyl complexesInfrared absorption spectrometry。staycarbon monoxideGas, C-O bond vibration (generally with νCOMeans) 2143cm in the spectrum-1Location of.νCOThere is a negative correlation between the position of C and the bond strength between metal and carbon.
material
position
CO
two thousand one hundred and forty-three
Ti(CO)six
one thousand seven hundred and forty-eight
V(CO)six
one thousand eight hundred and fifty-nine
Cr(CO)six
two thousand
Mn(CO)six
two thousand and one hundred
Fe(CO)six
two thousand two hundred and four
Fe(CO)five
2022, 2000
In addition to the vibration frequency, the number of ν CO in the spectrum can also be used to analyze the structure of complexes, octahedral complexes (such as Cr (CO))six）, whose spectrum has only one νCO。The spectra of complexes with weak symmetry will also be complex.
As Fetwo(CO)nineIn the spectrum of CO bondVibration frequencyIt appears at 208220191829cm-1。
ν can also be used in clustersCOSee the coordination mode of CO ligand.
Bridging (μtwo）Carbonyl ligand ofνCOIt will be 100-200cm lower than the common terminated carbonyl ligand-1。μthreeν of carbonyl ligand ofCOWill be lower.The following is ν of typical rhodium clustersCO：
In the reaction process, it is generally the negatively charged part of the nucleophilic reagent (that is, the nucleophilic part) advanced attack the unsaturated chemical bond in the substrate with a part of the positively charged end atom, and bond with it,pi bondDisconnect the anion intermediate that forms the atom at the other end, and then the electrophilic part of the reagent combines with the anion intermediate to form a nucleophilic addition product.
The most representative reaction is aldehyde or ketonecarbonylAndGrignard reagentAddition reaction: RC=O+R'MgCl → RR'C-OMgCl, and then hydrolysis to obtain alcohol, which is a good way to synthesize alcohol.In carbonyl group, O is slightly electronegative;In Grignard reagent, C-Mg is connected, Mg is slightly electropositive, and C is the nucleophilic site.Then the nucleophilic carbon of the Grignard reagent attacks the electrophilic carbonyl carbon, the double bond opens, and a new C-C bond is formed.
The carbonyl group can be added to nucleophiles with carbon as the central atom, such as Grignard reagent, HCN and sodium alkyne.
The carbonyl group can also be added to nucleophiles with nitrogen as the central atom, such as ammonia and its derivatives.
The addition of carbonyl group to nucleophiles with oxygen as the central atom, such as HtwoO. ROH, etc.
(2) Reaction application - growing carbon chain
The carbon chain is grown by nucleophilic addition reaction.
Grignard reagent contains magnesium halideOrganometallic compound, a class of nucleophilic reagents, is widely used in organic synthesis.
The deuterated hydrocarbon can be synthesized by Grignard reagent;Grignard reagent reacts with aldehydes, ketones, esters and epoxides to form corresponding alcohols;If the reaction generates secondary alcohol, it can also be oxidized to ketone, and then continue to react with Grignard reagent to generate tertiary alcohol.Grignard reagent can react with carbon dioxide to prepare carboxylic acid with one more carbon.
Reaction caused by α - active hydrogen
Carbon directly connected with functional group is calledα-Carbon, whileα-The hydrogen on the carbon isα-Hydrogen.α-The activity of hydrogen is affected by the functional group or substituent directly connected with it, which usually shows special reaction activity, and is more active than other hydrogen, so it is easier to have the characteristics and reactions of chemical reaction.
containα-In the presence of H aldehyde and dilute alkali, they can combine with each other to formβ-Hydroxaldehyde group, generated after heatingα、β-Unsaturated aldehydes (with a second α - H) form new carbon carbon bonds in the molecule through aldol condensation, which increases the carbon chain.
Aldehydes are easily oxidized, and many oxidants can oxidize aldehydes into acids.Fatty aldehydes are easier to oxidize than aromatic aldehydes.However, when aldehydes are exposed to the air, aromatic aldehydes are easier to oxidize than fatty aldehydes, because they are oxidized to ionic oxidation by chemical oxidants.
Ketone resists oxidation when encountering general oxidant.When ketone encounters strong oxidant, the carbon chain breaks and forms acid.When ketones are oxidized, the carbon carbon bond breaks and generally forms a mixture, which is of little significance. However, after the oxidation of cycloketones, a single compound can be obtained, which is of significance in preparation.
Ketones can undergo a special oxidation reaction: Bayer Villiger oxidation, that is, ketones are oxidized by peroxide, the carbon chain directly connected to the carbonyl group breaks, and an oxygen is inserted to form an ester.[2]
(2) Reduction reaction
Aldehydes and ketones can be reduced to alcohols by catalytic oxidation under certain conditions, but it should be noted that some reactions can only be carried out under heating, pressure or special catalysts;The most commonly used solvent is alcohol;If the stereo environment on both sides of the carbonyl group is different, the catalyst is usually adsorbed from the side with low air resistance for cis hydrogenation.
Aromatic aldehydes withα-Aliphatic anhydride of H, co heated in the presence of corresponding carboxylate, generates condensationα，β-Unsaturated acid, this reaction is called Perkin reaction.
The condensation reaction between aldehyde (ketone) containing α - H and the hydrochloride of formaldehyde and ammonia (or 1 ° amine, 2 ° amine) is called Mannich reaction.
The net result of this reaction is that dimethylaminomethyl substitutedα-H. Therefore, it is also called ammonia methylation reaction, and the product is β - aminoketone.
Mannich reaction is usually carried out in acidic solution. Except aldehyde and ketone, other reactions includeα-Compounds of H, such as esters and nitriles, can also undergo this reaction.[2]
Preparation method
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Prepared from alcohol
Carbonyl compounds can be prepared by directly oxidizing alcohols with oxidants, such as Pfitzner Moffatt oxidation, the method of using DCC and DMSO as oxidants to oxidize primary or secondary alcohols into corresponding aldehydes or ketones[6]。
Preparation of oxidized alcohol
Prepared from unsaturated hydrocarbon
Carbonyl compounds such as aldehydes and ketones can be synthesized by direct water and alkynes or direct oxidation of alkenes[5]。
Direct oxidation of olefin synthesis
Prepared from aromatic hydrocarbon
For example, through the Friedel Crafts acylation reaction, aromatic hydrocarbons and acyl halides or anhydride can be electrophilically substituted to form carbonyl compounds under the catalysis of proton acid or Lewis acid[4]。
