9394949438

[LATEST]$type=sticky$show=home$rm=0$va=0$count=4$va=0



ALDEHYDES AND KETONES

Aldehydes and Ketones are characterised by the presence of Carbonyl group >C = O in their molecules. Aldehydes contain group and ketones the . If the groups attached to carbonyl carbon are the same, the ketone is symmetrical and if they are different the ketone is unsymmetrical.

NATURE OF CARBONYL GROUP

The carbon and oxygen of the carbonyl group are sp2 hybridised and the carbonyl double bond is made of one s bond and one p bond.
 or  
The electronegativity of oxygen is much higher than that of carbon, the p electron cloud is displaced towards the oxygen. Therefore the C–O bond is polar in nature and carbonyl compounds possess dipole moment (2.3 to 2.8 D)

NOMENCLATURE OF ALDEHYDES

There are two systems
  • Common system : The suffix “-ic acid” is replaced by the suffix “-aldehyde
  • IUPAC system : The suffix “-e” of alkane is replaced by the suffix “-al”.
Compound Common name IUPAC name
HCHO Formaldehyde Methanal
CH3CHO Acetaldehyde Ethanal

NOMENCLATURE OF KETONES

  • Common system : Symmetrical ketones are named as dialkyl ketone and name of unsymmetrical ketone is obtained by naming the alkyl groups alphabetically and adding the third word ketone.
  • IUPAC system : The suffix “-e” of corresponding alkane is replaced by “-one
Compound Common name IUPAC name
H3C.COCH3 dimethyl ketone (acetone) Propanone
H3C.COC2H5 ethyl methyl ketone butanone
In higher ketones the numbering of C-atoms is must to show the position of carbonyl group. eg. :
3-hexanone
2-methyl-4-heptanone

ISOMERISM IN ALDEHYDES

Aldehydes exhibit two types of isomerism

Chain isomerism

Functional isomerism

ISOMERISM IN KETONES

They exhibit three types of isomerism
Chain isomerism
Functional isomerism
Position isomerism

GENERAL METHODS OF PREPARATION OF ALDEHYDES

  • Controlled oxidation of primary alcohols
    Oxidising agents K2Cr2O7/H2SO4 or KMnO4/H2SO4
PCC is pyridinium chlorochromate known as Collin’s reagent and is specific for oxidation of 1º alcohol to aldehyde.
  • Dehydrogenation of primary alcohol
  • By Rosenmund reduction from acid chloride
  • Hydration of Alkynes (Kucherov reaction)
  • Reductive ozonolysis of alkenes
  • Distillation of Calcium salt of fatty acid with calcium formate
  • From acid
  • Waker’s process
  • Oxo process
  • Stephen’s reduction of nitriles :
  • Hydrolysis of Geminal halides
     
  • From Glycols
  • From Grignard’s reagent
  • From acid chloride by the use of lithium t-butoxy aluminium hydride

GENERAL METHODS OF PREPARATION OF KETONES ONLY

  • Oxidation of 2º alcohol
    Oxidising agent K2Cr2O7/H2SO4 or KMnO4/H2SO4
  • Dehydrogenation of 2º alcohols
  • Hydration of alkynes
  • Reductive ozonolysis of alkenes
  • From Calcium salt of an acid
  • From acid
  • Hydrolysis of non-terminal gem.halide
  • From Grignard’s reagents
  • From acid chlorides

PHYSICAL PROPERTIES

  • Formaldehyde is a gas and its 40% aqueous solution was known as formalin but now it is 40% HCHO, 8% CH3OH, 52% H2O. They are polar in nature and have higher values of b.p. Lower members are soluble in water.
  • Lower aldehydes and ketones (C1 – C4) are soluble in water due to presence of H–bonding.
        
  • Reactivity
It is due to + I effect of alkyl groups which decreases the +ve charge on carbonyl carbon.

Steric hindrance : The bulky alkyl group hinder the approach of nucleophile.
a-hydrogen atom is acidic in nature due to Resonance

CHEMICAL PROPERTIES

ADDITION REACTIONS

Their addition reactions are known as nucleophilic addition reactions

The followings reaction in different ways with NH3
  
It is used as urinary antiseptic.

NUCLEOPHILIC ADDITION REACTIONS WITH ELIMINATION OF WATER MOLECULE

The control of pH is must for these reactions. The optimum value is around 3.5.

Control of pH during formation of ammonia derivatives :
At low pH : H+ concentration is very high. The carbonyl compound and ammonia derivative, both protonated and latter cannot act as nucleophile .
At high pH :  H+ concentration is too small. The protonation of carbonyl group will not occur and reaction will not occur smoothly.
Hence, optimum pH of the medium is around 3.5.

OXIDATION

Ketones are oxidised by strong oxidising agents such as Conc. HNO3, K2Cr2O7/H2SO4, KMnO4/H2SO4

OXIDATION WITH SeO2
The CH3 group adjacent to  is oxidised to – CHO and >CH2 group is oxidised to
>C = O group.

POPOFF’S RULE
During oxidation of unsymmetrical ketone the carbonyl group is retained by smaller alkyl group.
(major products)
Jone’s reagent : Acidified K2Cr2O7 i.e. chromic acid and sulphuric acid mixture

HALOFORM REACTION
Oxidation of acetaldehyde or methyl ketones with Sodium Hypohalite (NaOX) or (X2 + NaOH) gives haloform CHX3. The reaction is of practical value to identify these compounds by forming CHI3.

BAYER-VILLIGER OXIDATION
Oxidation of aliphatic Ketones by organic per acids, e.g. perbenzoic acid, peracetic acid or monoperthalic acid to form esters or their hydrolysed products

REDUCTION 

CONDENSATION REACTIONS

ALDOL CONDENSATION
Aldehydes and Ketones having at least one a-hydrogen atom in presence of dil. alkali give b- hydroxy aldehyde or b-hydroxy ketone, which on heating gives a,b-unsaturated carbonyl compound.

CROSSED ALDOL CONDENSATION


INTRAMOLECULAR ALDOL CONDENSATION

CANNIZZARO’S REACTION
Aldehydes containing no a-hydrogen atom on warming with 50% NaOH or KOH undergo disproportionation i.e. self oxidation - reduction known as cannizzaro’s reaction.
* 2-methyl propanal (CH3)2CH.CHO has a-hydrogen atom but gives Cannizzaro’s reaction.
Aldehydes containing a-H atoms on heating with conc. alkali give brown resinous mass by undergoing repeated aldol condensation.

CROSSED CANNIZZARO’S REACTION

TISHCHENKO REACTION
Aldehydes containing a-hydrogen atom with aluminium ethoxide give esters.

REFORMATSKY REACTION
It is the reaction between an a-bromo acid ester and a carbonyl compound (aldehyde or ketone) in the presence of zinc to form a b-hydroxy ester.

BECKMANN’S REARRANGEMENT
It is rearrangement of keto oxime to N-substituted acid amide in presence of Conc. H2SO4, PPA, SOCl2, PCl5 etc.

CONDENSATION PRODUCTS OF ACETONE
Above reactions are not aldol condensations.

POLYMERS OF FORMALDEHYDES

POLYMERS OF ACETALDEHYDE

BENZALDEHYDE (AROMATIC ALDEHYDES)

PREPARATION

  • Etard’s oxidation
  • Oxidation of toluene
  • Gattermann Koch Synthesis
(Combination of CO + HCl act as formyl chloride HCOCl)
It is an electrophilic substitution reaction, the electrophile is  formylium ion.
  • Gattermann aldehyde synthesis
  • From benzyl chloride (Lab method)
  • Rosenmund reaction
  • Vilsmeyer reaction
  • From Grignard’s reaction
  • From Benzal chloride (manufacture)
  • Partial oxidation of toluene (manufacture)

PHYSICAL PROPERTIES

Colourless, highly refractive liquid b.p. 443K. It has smell of bitter almonds, slightly soluble in water. Steam volatile and poisonous.

CHEMICAL PROPERTIES

REACTION OF CHO GROUP GIVEN BY AROMATIC ALDEHYDES
           
   

REACTIONS DUE TO BENZENE NUCLEUS
CHO group is meta directing with deactivation of benzene nucleus

Benzaldehyde reduces Tollen’s reagent but not Fehling solution.

USES

  • As flavouring agent
  • In perfumes
  • Manufacture of triphenylmethane dyes

ACETOPHENONE (AROMATIC KETONES)

PREPARATION

  • By Friedel Craft’s acylation
  • From benzaldehyde
  • Manufacture

PHYSICAL PROPERTIES

It is colourless crystalline compound m.p. 20ºC, b.p. 202ºC.
At room temperature it is coloured liquid.

CHEMICAL PROPERTIES

  • Reactions due to . It gives almost all reactions due >C = O group.
  • Reactions due to benzene nucleus : –COCH3 is meta directing in nature. Hence electrophilic substitution reactions give meta derivative.
  • It give iodoform test.
  • Some important reactions are :
Its vapour attack nose, throat and lungs. It is used as tear gas.

USES

It is used as hypnotic in medicine.

TEST FOR ALDEHYDE

  • Tollen’s reagent (ammoniacal silver nitrate). All aldehydes give silver mirror.
  • Fehling Solution (alkaline solution of Cu2+ complexed with Sodium potassium tartrate blue colour). All aldehydes give red colour except benzaldehyde.
  • Benedict’s solution (Copper sulphate, sodium citrate and sodium carbonate solution). Aldehydes give reddish brown ppt.
  • Schiff’s reagent (dilute solution of p-rosaniline hydrochloride decolourised with SO2 or H2SO4). Aldehydes give pink colour.
Acetone respond to this test slowly and o-hydroxy benzaldehyde does not give pink colour with schiff’s reagent

Note : Formic acid, tartaric acid, a-hydroxy ketones, glucose, fructose reduce  Tollen reagent and Fehling solution.

Want to know more

Want to Know More
Please fill in the details below:

INNER POST ADS

Latest IITJEE Articles$type=three$c=3$author=hide$comment=hide$rm=hide$date=hide$snippet=hide

Latest NEET Articles$type=three$c=3$author=hide$comment=hide$rm=hide$date=hide$snippet=hide

Name

Alternating Current,60,Basic Maths,2,best books for iit jee,2,best coaching institute for iit,1,best coaching institute for iit jee preparation,1,best iit jee coaching delhi,1,best iit jee coaching in delhi,2,best study material for iit jee,4,Blog,62,books for jee preparation,1,books recommended by iit toppers,3,Capacitance,3,CBSE NEET,9,cbse neet 2019,3,CBSE NEET 2020,1,cbse neet nic,1,Centre of Mass,2,Chemistry,58,Class 12 Physics,15,coaching for jee advanced,1,coaching institute for iit jee,2,Collision,2,Current Electricity,4,Electromagnetic Induction,3,Electronics,1,Electrostatics,3,Energy,1,Fluid Mechanics,4,Gravitation,2,Heat,4,iit admission,1,iit advanced,1,iit coaching centre,3,iit coaching centre in delhi,2,iit coaching classes,2,iit coaching in delhi,1,iit coaching institute in delhi,1,iit entrance exam,1,iit entrance exam syllabus,2,iit exam pattern,2,iit jee,4,iit jee 2019,3,iit jee advanced,2,iit jee books,3,iit jee coaching,2,iit jee exam,3,iit jee exam 2019,1,iit jee exam pattern,3,iit jee institute,1,iit jee main 2019,2,iit jee mains,2,iit jee mains syllabus,2,iit jee material,1,iit jee online test,3,iit jee practice test,3,iit jee preparation,6,iit jee preparation in delhi,2,iit jee preparation time,1,iit jee preparation tips by toppers,2,iit jee question paper,1,iit jee study material,3,iit jee study materials,2,iit jee syllabus,2,iit jee syllabus 2019,2,iit jee test,3,iit preparation,2,iit preparation books,5,iit preparation time table,2,iit preparation tips,2,iit syllabus,2,iit test series,3,IITJEE,100,JEE Advanced,82,jee advanced exam,1,jee advanced exam pattern,1,jee advanced paper,1,JEE Books,1,JEE Coaching Delhi,3,jee exam,3,jee exam 2019,6,JEE Exam Pattern,2,jee exam pattern 2019,1,jee exam preparation,1,JEE Main,85,jee main 2019,4,JEE Main application form,1,jee main coaching,1,JEE Main eligibility criteria,3,jee main exam,1,jee main exam 2019,3,jee main online question paper,1,jee main online test,3,jee main registration,2,jee main syllabus,2,jee mains question bank,1,jee mains test papers,3,JEE Mock Test,2,jee notes,1,jee past papers,1,JEE Preparation,2,jee preparation in delhi,1,jee preparation material,4,JEE Study Material,1,jee syllabus,6,JEE Syllabus Chemistry,1,JEE Syllabus Maths,1,JEE Syllabus Physics,1,jee test series,3,Kinematics,1,Latest article,1,Latest Articles,61,latest news about neet exam,1,Laws of Motion,2,Magnetic Effect of Current,3,Magnetism,3,Modern Physics,1,NCERT Solutions,15,neet,2,neet 2019,1,neet 2019 eligibility criteria,1,neet 2019 exam date,2,neet 2019 test series,2,NEET 2020 Eligibility Criteria,1,neet application form 2019 last date,1,Neet Biology Syllabus,1,Neet Books,3,neet eligibility criteria,3,neet exam 2019,7,neet exam application,1,neet exam date,1,neet exam details,1,neet exam pattern,6,neet exam pattern 2019,2,neet examination,1,neet mock test 2019,1,Neet Notes,3,Neet Online Application Form,3,neet online test,2,neet past papers,1,neet physics syllabus,1,neet practice test,2,NEET preparation books,1,neet qualification marks,1,NEET question paper 2019,1,neet question papers,1,neet registration,1,Neet Study Material,3,neet syllabus,6,neet syllabus 2019,5,NEET Syllabus 2020,1,neet syllabus chemistry,1,neet syllabus for biology,1,neet syllabus for physics,1,neet test series,1,neet ug 2019,2,news,1,online study material for iit jee,1,Optical Instruments,1,Physics,110,physics books for iit jee,1,Power,1,Practical Physics,1,Ray Optics,1,Rotational Motion,3,SHM,3,Simple Harmonic Motion,3,study materials for iit jee,1,Study Notes,110,study notes for iit jee,1,Thermodynamics,4,Units and Dimensions,1,Vectors,2,Wave Motion,3,Wave Optics,1,Work,1,
ltr
item
Best Coaching Institute in Delhi for IIT JEE, NEET, AIIMS, PMT - Clear IIT Medical: Aldehydes and Ketones | Chemistry Notes for IITJEE/NEET
Aldehydes and Ketones | Chemistry Notes for IITJEE/NEET
https://lh3.googleusercontent.com/uNAADoXGcSVxUgeXm-EgdPPLHsETpDQx0A9GSJ-DWHd8ckWb9i-VmhJQU0aLDfMJg8fLwDjhxboZ7-WCSJzR8XP__-FGnltt_u_OMedkogzXMnccJay2cwANdrLzmCt0a1l0WNW27cpl1p3ISw
https://lh3.googleusercontent.com/uNAADoXGcSVxUgeXm-EgdPPLHsETpDQx0A9GSJ-DWHd8ckWb9i-VmhJQU0aLDfMJg8fLwDjhxboZ7-WCSJzR8XP__-FGnltt_u_OMedkogzXMnccJay2cwANdrLzmCt0a1l0WNW27cpl1p3ISw=s72-c
Best Coaching Institute in Delhi for IIT JEE, NEET, AIIMS, PMT - Clear IIT Medical
https://www.cleariitmedical.com/2019/04/chemistry-notes-aldehydes-ketones.html
https://www.cleariitmedical.com/
https://www.cleariitmedical.com/
https://www.cleariitmedical.com/2019/04/chemistry-notes-aldehydes-ketones.html
true
7783647550433378923
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS CONTENT IS PREMIUM Please share to unlock Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy