Organic Flashcards
alkynes general formula
CnH2-2
reactivity of alkanes, alkenes and alkynes.
Alkene>Alkyne>Alkane.
.alkene has electrons more exposed for attack
.pi bond is weak
.alkyne short bondlength
.alkane have inert sigma bonds and is nonionic.
paraffins also known as?
alkanes
preparation of alkynes(2 methods)
1.Dehydrohalogenation of Vicinal dihalide (R-C2H2X2-R) {elimination}
- Dehalogenation of Tetrahalides [zn metal used]
alkynes addition reactions
1.hydrogenation [ni/pt]
“triple bond to c=c then c-c”
2.hydrohalogenation [addition of hx]
“ethyne turns into vinyl bromide and then 1,1 dibromoethane”
3.hydration [HgSO4/H2SO4]
“ethyne gives acetaldehyde. rest give ketones”
acidic nature of alkynes used to distinguish bw
used to distinguish between
.alkynes and alkenes
.Terminal alkyne from other alkynes
ethyne reaction with sodamide [NaNH2] in liq. NH3 (ammonia).
Formation of Sodium acetylide(used for chemical synthesis)
R-C—CH + NaNH2—–liq NH3——->R-C—CNa +NH3
HC—CH + 2Na—–> NaC—Cna + H2
[sodium acetylide]
how acetylides of copper and silver obtained?
passing acetylene (C2H2) in ammonical sol of cuprous chloride (Cu2Cl2) and THEN silver nitrate solution (NH4OH)
phenol reactions due to -OH group
- salt formation (with NaOH)
2.Ester formation (with alkaline/ Acetyl chloride)
3.reduction with zn (forms benzene +ZnO)
addition reactions of phenol
- Nitration (dil. HNO3) forms ortho and para nitrophenol
(conc HNO3) forms Picirc acid.(2,4,6 trinitrophenol)
2.hydrogenation (removes inner ring)
- halogenation (electrophillic sub)
produces 2,4,6 tribromophenol [White ppt] - Sulfonation[conc H2SO4]
produces Hydroxybenzene sulfonic acid.
base catalyzed reactions of Aldehydes/Ketones
- HCN (all ald/ketone)
produces cyanohydrins which, on hydrolysis of triple bond makes a-hydroxyacids.
2.sodium bisulphite NaHSO3 (only methyl ketones)
white ppt produced
3.Aldol condensation
aldol on heating with dil.acid produces Crotonaldehyde
4.Canizzaro’s reaction (self redox)
{aldehydes with no a-hydrogen react with alkali to form -OH and -COOH}
acid catalysed (Aldehydes/ketones)
1.Ammonia derivatives
{addition elimination}
2.Hydroxylamine(NH2OH)
{form OXIMES}
3.Phenylhydrazine
{form phenyl hydrazones}
4.Hydrazine NH2NH2
{form hydrazones}
identification of carbonyl compounds
1.only aldehydes
2.only ketones
3.both
4.only methyl ketones
1.tollens-silver mirror
Fehlings-red
benedit-brick red ppt of cuprous chloride
2.Sodium Nitroprusside-red
- 2,4-DNPH
- Sodium Bisulphite-White ppt
trihaloalknes
alkanes with three halogen atoms
alkyl halides are dihaloalkanes?
NO. monohaloalkanes.
secondary alkyl halide
halogen atom attached to a carbon that is further attached to 2 carbon atoms
B elimination reaction
removal of hydrogen and halogen from adjacent carbon atoms of alkyl halide.
b-hydrogen is necessary for elimination.
strong bases such as OH, NH2 cause elimination in preference to substitution
E1 AND E2 REACTIONS
*same order of reactivity as SN1 AND SN2
E1 is two step reaction in which ionisation of alkyl halide and nucleophile attacks on b hydrogen in second step
[rate of reaction depends on conc of alkyl halide]
order; tertiary>secondary>primary
E2 single step.attack of nucleophile and removal of leaving group at the same time.
[rate dependant on alkyl halide and base]
order; primary>secondary>tertiary
alkyl halides :substitution or elimination conditions
substitution is more favourable energetically
as elimination only occurs in presence of b hydrogen.
> primary alkyl halides favour substitution
> tertiary haloalkanes favour elimination because approach to a carbon is difficult for substitution
> strong bases favour elimination too. in presense of a strong base, main reaction is elimination and substitution is a side reaction.
> elimination is favoured more than by substitution by decreasing solvent polarity.
alcoholic KOH affects elimination while polar aq KOH used for substitution.
> increase in temperature favours elimination because less reorganization of bonds
Test for identification bw alcohols
Lucas test (HCl in ZnCl2)
Immediate oily on 3⁰ alcohols
5 min 2⁰
On heat 1⁰
Preparation of aldehydes and ketones
(Pg331ch12)
1.Formaldehyde
Lab method
passing a mixture of Methanol vapours over PT ASBESTOS AT 300⁰C
Industrial
passing a mixture of methanol vapours and air over silver catalyst 500⁰C
- Acetaldehyde
Lab method
Oxidation of ethyl alcohol with H+/Na2Cr2O7 - Acetone
Prepared by dry distillation of calcium acetate.
Aliphatic carboxylic acids
CarboxylicAcids attached with a H or an alkyl (R group)
Aliphatic carboxylic acids
CarboxylicAcids attached with a H or an alkyl (R group)
Preparation of carboxylic acids by?
- Oxidation of 1⁰ alcohols
- Hydrolysis if alkane nitriles C—N
- Grignard reag(MgX) with CO²
- Ester hydrolysis
- Oxidation of alkenes
Preparation of carboxylic acids by?
- Oxidation of 1⁰ alcohols
- Hydrolysis if alkane nitriles C—N
- Grignard reag(MgX) with CO²
- Ester hydrolysis
- Oxidation of alkenes
