Haloalkanes And Haloarenes Flashcards
Which is most stable radical? Pg 88 qus 16
Allyl free radical is highly stable due to hyperconjugation
Preparation of alkyl halides from alkenes follow which mechanism?( Markovnikov rule)
Electrophilic addition and carbocation intermediate formation
Anti markovnikov rule follows which mechanism
Free radical addition
How can you prepare alkyl iodide
By halogen exchange method
Finkelstein reaction
In presence of acetone
Wat type of reaction is Finkelstein reaction
Nucleophilic substitution (SN2)
nacL / nabr being insoluble in acetone shift the equilibrium forward
How can you prepare alkyl fluorides
By swarts reaction
In presence of heavy metal fluorides ( ex - SbF3. Hg2F2 AgF)
Characteristic reactions of haloalkanes is
Nucleophilic substitution reaction
Wat is darzen’s process
Most preferred to prepare alkyl chloride
Uses thinoyl chloride (SOCL2)
Lucas reagent? Wat is use of lucas test?
Anhydrous ZnCL2. + Conc HCL
Lucas test distinguishes between primary secondary and tertiary alcohol
Primary mein turbidity mein time lagta
Tertiary mei nhi lagta
Wat is goorves precess
Reaction of alcohol with HCL to form alkyl halides in presence of anhydrous ZnCL2
Dipole moment of alkyl halides
R-CL. > R-F> R-Br > R-I
Although reactivity and boiling point RI ki sabse zyada
Why is grignard’s reagent prepared under anhydrous conditions?
Coz GR reacts with any source of acidic H to give alkane (ie reduction)
Which is the best departing halide?
Iodide
Ambidentate nucleophiles
CN- and NO2-
Posses two nucleophilic centres
Wat is williamson synthesis?
Preparation of ether (R-O-R’) from alkyl halide in presence of sodium alkoxide ie (R’O-Na+)
R-X with KCN will give?
R-CN ie alkyl cyanide
R-X with AgCN will give?
R-NC ie alkyl isocyanide or carbyl amine
RX with KNO2 will give?
R-ONO ie alkyl nitrite
RX with AgNO2 will give
R-NO2 ie nitro alkane
Tell about SN1 reaction
Rate only depends on concentration of alkly halide
Occur in polar protic solvents like water coz hydration energy se carbocation stable hote!!
Occurs in two steps. First is slow and rds and carbocation intermediate is formed
Reactivity of alkly halides in SN1
3° > 2°> 1° one to sn1 dikhate hi nhi
This order is due to carbocation stability
Benzylic and allylic halides prefer which nucleophilic substitution mechanism?
SN1 coz their carbocations are resonance stabilised
Tell about SN2
Occur in single step
Complete inversion of configuration ie Walden inversion
In polar aprotic like dmf dmso
Rate depends on both nucleophile and alkyl halide ki concentration
Give reactivity order for alkyl halide in SN2
1°>2°>3° due to steric hindrance
Wat are expections to styzeff rule
If the base is bulky.. Hoffmann is major
If hindrance around beta hydrogen is large then Hoffmann
In case of Alkyl fluorides Hoffman is always major (mechanism E2)
In which conditions is elimination preferred over substitution
When base(nucleophile )is bulky
When base is strong like OH- NH2-
When large steric hindrance in alkyl halide
Reaction conditions like high temperature
Do primary alkyl halide prefer substitution or elimination?
Primary prefer substitution
While
Tertiary prefer elimination
(Due to steric hindrance)
Agar steric hindrance hogi to elimination prefer kiya jaata hai
Wat is solvolysis
A reaction in which the substrate reacts with the solvent
Which indergoes nucleophilic substitution exclusively by SN1
Benzyl chloride
Boiling point of ortho para Meta ie aryl halides
Nearly the same but
O> p> m
Melting point of arly halides
Para has much higher melting point.
P» o> m
Orientation of attacking electrophile is governed by which effect?
+R effect
Incoming electrophile attacks which positions?
Ortho and para
Why don’t aryl and vinylic halides give nucleophilic substitution reaction under normal conditions
Partial double bond character of c-x bond
C(sp2)-x bond length is short and hence difficult to break
Wat is the effect of EWG on reactivity of arly halides in nucleophilic substitution
EWG at ortho and para increases reactivity by stabilising the intermediate carbanion
Wat is NBS
N bromo succinimide
Most preferred reagent for bromination of allylic free radical subsi .. taaki addition na ho coz ye limited bromine hi provide krega
Chloropicrin is obtained by the reaction of
Nitric acid on chloroform
Nbs is a specific reagent for?
Allylic substitution
N bromo succinimide
