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Friday, 19 July 2019

Physical properties of alcohols

Physical properties of alcohols

i) Lower members of alcohol are colourless liquid & have distinctive smell but higher members are colourless solid.
ii) Alcohols have more boiling point than alkane, alkyl halide, aldehydes, ketones & ether due to polar bond it forms inter molecular hydrogen bonding, which requires more energy to break hydrogen bonding.
iii) The boiling point of alcohol increases as carbon atom increases due to increase in Van der Waals forces. But as branching in alcohol increases the boiling point decreases.
iv) Lower member are more soluble in water due to hydrogen bonding between alcohol & water. But as the size of alkyl group increases in alcohol the solubility decreases. Boiling point increases as number of –OH group in alcohol molecules increases. 


Thursday, 13 June 2019

Structure of alcohol

Structure of alcohol

        In alcohols, the oxygen of the –OH group is attached to carbon by a sigma (σ) bond formed by the overlapping of a sp³ hybridised orbital of carbon with a sp³ hybridised orbital of oxygen. The bond angle in alcohols (108.9) is slightly less than the tetrahedral angle (109).  It is due to the repulsion between the unshared electron pairs of oxygen. 
        Figure  depicts structural aspects of methanol. The bond length between C–O is 142 pm & O–H is 96 pm.

Monday, 3 June 2019

Coordination compounds / complex

Coordination compounds 

Salient features of CFT
Application of CFT on octahedral complexes
Application of CFT on tetrahedral complexes⟶  
Spectrochemical series⟶
Valence bond theory⟶ 
Salient features of VBT
Structure of complex compounds based on valence bond theory⟶ 
   1) Structure of Nickel tetracarbonyl (Ni(CO))
   2) Formation of Ni(Cl)⁻² 
   3) Structure of Ni(CN)⁻²
   4) Structure of cuproammonium sulphate 
        (Cu(NH₃)SO)
   5) Structure of [Co(NH)]³⁺ 

 Isomerism in coordination compounds⟶ 
Geometrical isomerism in complexes with coordination number (C.N.) 4
Geometrical isomerism in complexes with coordination number (C.N.) 6
Optical isomerism
Complex ion
Coordination entity
Coordination sphere
Oxidation number of central metal atoms
Homoleptic & heteroleptic complexes
Types of complexes
Charge number of a complex ion

Ligands & its classification⟶
   a) Mono / unidentate ligands
   b) Poly / multidentate ligands
       Bidentate ligands
       Tridentate ligands
       Tetradentate ligands
       Hexadentate ligands
       Chelating ligands   
       Ambidentate ligands

Werner's theory in the light of modern electronic theory of valence⟶  
Application of Werner's theory on Co(III) amines complex
Experimental observations of Werner's theory
Download PDF coordination compounds⟶
 

Saturday, 1 June 2019

Halogen derivatives of alkanes & arenes

Halogen derivatives of alkanes & arenes 

Introduction⟶
Classifications
Monohalogen derivatives of alkanes
Classification of alkyl halides (on the basis of types of carbon)
Nomenclature of alkyl halides
Nature of CーX bonds in alkyl halide

Preparations of alkyl halides
1) From alkanes by halogenations
2) From alkenes by hydrogen halides⟶  
   Markownikoff's rule⟶ 
   Peroxide effect / Anti-Markownikoff's rule⟶ 
3) From alcohols⟶ 
   a) Reaction with hydrogen halides (to form alkyl 
       chloride, alkyl bromide & alkyl iodide)
   b) By phosphorous halides⟶
 C) Reaction with thionyl chloride (Sulphonyl chloride)⟶
 4) By halogen exchange method ⟶
    (Finkelstein reaction & Swarts reaction)  

Physical properties of alkyl halides⟶
Chemical properties of alkyl halides⟶ 
   a) Substitution reaction
      i) Formation of alcohols by hydrolysis
      ii) Reaction with moist silver oxide⟶
      iii) Formation of alkyl cyanides / alkane nitrliles  
      iv) Formation of alkyl isocyanides⟶ 
     v) Formation of primary amines (Ammonolysis)⟶  
     vi) Formation of ethers (Williamson's synthesis)⟶
      vii) Formation of esters⟶

   b) Elimination reaction
      i) Dehydrohalogenation reaction (Saytzeff's rule)
   
   C) Reaction with metals
      i) Reaction with Na metal 
         (Wurtz reaction / Formation of higher alkanes)
      ii) Reaction with Mg metal
         (Formation of Grignard reagent i.e. RMgX)

Nucleophilic Substitution  (SN1 & SN2)⟶
Ordinary light, monochromatic light, plane polarized light, optical activity, optically active molecules.

Criteria for optical activity⟶ 
Reaction mechanism for SN₁⟶ 
Stereochemistry of SN₁
Reaction mechanism for SN
Stereochemistry of SN
Bezylic halides & allylic halides

Comparison between SN & SN₂⟶

Friday, 31 May 2019

Alcohol preparation by Grignard reagents

Alcohol preparation methods by Grignard reagents

         Alcohols are produced by the reaction of Grignard reagents with aldehydes and ketones.
     The first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group to form an adduct. Then hydrolysis of the adduct yields an alcohol.

Alcohol preparation methods by grignard reagent


i) When methanal reacts with methyl magnesium iodide in presence of dry ether to give complex which on acid hydrolysis gives ethanol.


ii) When ethanal reacts with methyl magnesium iodide in presence of dry ether to give complex which on acid hydrolysis gives propan–2–ol.



iii) When propanone reacts with methyl magnesium iodide in presence of dry ether to give complex which on acid hydrolysis gives 2–methylpropan–2–ol.




Alcohol preparation methods by grignard reagent


Alcohol preparation methods by grignard reagent

Friday, 24 May 2019

Alcohol preparation

 Alcohol preparation

From carbonyl compounds (by reduction): 

       Aldehydes can be reduced into primary alcohols & ketones can be reduced into secondary alcohols in presence of catalyst. If ethanal is reacted with H in presence of catalyst Ranyl Ni then ethyl alcohol is formed.


      Aldehydes or ketones also reacted with nascent hydrogen in presence of sodium amalgam (Na – Hg) in water gives alcohol.

         It is also prepared by treating aldehydes & ketones with sodium borohydride (NaBH) or lithium aluminium hydride (LiAlH). Aldehydes yield primary alcohols whereas ketones give secondary alcohols. LiAlH is more reactive than NaBH. LiAlH reacts with water violently hence solvent dry ether or tetrahedral furan required. NaBH & LiAlH donate hydrides hence separate hydrolysis required after reduction. LiAlH reduced only carbonyl group & not unsaturated carbon double bond, hence used to prepare unsaturated alcohols, as follow,

       Carboxylic acids & esters are reduced to primary alcohols by lithium aluminium hydride, a strong reducing agent.

      Esters are more easily reduced than carboxylic acid & form two molecules of alcohols.

    
      When carboxylic acids & alcohols react in presence of acid forms ester then further catalytic hydrogenation forms alcohols.

neet solved papers 2019

  NEET solved paper 2019 (Q. 33 to 44)


33) Match the Xenon compounds in Column-I with its structure in Column-II and 
     assign the correct code: 
 Ans:
 

         Since XeF is square planar (hence a-ii) & XeF is octahedral here is distorted octahedral (hence b-iii). These two options are matched in (2). 

 34) The manganate and permanganate ions are tetrahedral, due to:
  (1) The π-bonding involves overlap of p-orbitals of oxygen with d-orbitals of manganese
  (2) There is no
π-bonding
  (3) The
π-bonding involves overlap of p-orbitals of oxygen with p-orbitals of manganese
  (4) The
π-bonding involves overlap of d-orbitals of oxygen with d-orbitals of manganese 

Ans: 
   (1) The π-bonding involves overlap of p-orbitals of oxygen with d-orbitals of manganese


35) Which of the following species is not stable?
  (1) [SiF]²⁻
  (2) [GeCl
]²⁻
  (3) [Sn(OH)]²⁻
  (4) [SiCl]²⁻  

Ans:   
   (4) [SiCl]²⁻ 
         In group 14 elements, except carbon, Si, Ge, Sn & Pb contain d-orbital. Hence form species like [SiF]²⁻, [GeCl]²⁻ & [Sn(OH)]²⁻ . But the size of chloride ion is large & Si does not accommodate 6 chloride hence [SiCl]²⁻ is not unstable.

36) For a cell involving one electron E°cell= 0.59 V at 298 K, the equilibrium constant 
     for the cell reaction is:
  (1) 1.0 × 10²
  (2) 1.0 × 10
 (3) 1.0 × 10¹º
 (4) 1.0 × 10³º

Ans.:
  (3) 1.0 × 10¹º


37) Which of the following is an amphoteric hydroxide?
  (1) Sr(OH)
  (2) Ca(OH)
  (3) Mg(OH)
 (4) Be(OH)
Ans: 
     (4) Be(OH) 
   
38) A gas at 350 K and 15 bar has molar volume 20 percent smaller than that for an 
   ideal gas under the same conditions. The correct option about the gas and its 
   compressibility factor (Z) is:  
  (1) Z > 1 and attractive forces are dominant
  (2) Z > 1 and repulsive forces are dominant
  (3) Z < 1 and attractive forces are dominant
  (4) Z < 1 and repulsive forces are dominant
 

Ans: 
    (3) Z < 1 and attractive forces are dominant
39) A compound is formed by cation C and anion A. The anions form hexagonal 
   close  packed (hcp) lattice and the cations occupy 75% of octahedral voids. The 
   formula of the compound is: 
  (1) CA
  (2) CA
  (3) CA
  (4) CA 

Ans:
   (3) CA

40) In which case change in entropy is negative? 
  (1) Evaporation of water
  (2) Expansion of a gas at constant temperature
  (3) Sublimation of solid to gas
  (4) 2H(g) ⟶ H
(g)

Ans: 
    (4) 2H(g) ⟶ H(g)
    Entropy means molecular disorder. In options (1) to (3) molecular disorder or randomness increase but in option (4) molecular disorder decreases due to decrease in number of moles of H(g) atoms.
  
41) Which of the following series of transitions in the spectrum of hydrogen atom fall 
     in visible region?  
  (1) Lyman series
  (2) Balmer series
  (3) Paschen series
  (4) Brackett series 


Ans.:  
     (2) Balmer series
   Lyman series (n=1) are in U.V. of wave length 10nm—400nm.
  Balmer series (n=2) are in visible region of wave length more than 400nm but less than 700nm.
  Paschen series (n=3) are in I.R. region of more wave length up to 1050nm, generally invisible to human eye. 

   Brackett series (n=4) & pfund (n=4).

42) The method used to remove temporary hardness of water is:  (1) Calgon's method
  (2) Clark's method
  (3) Ion-exchange method
  (4) Synthetic resins method


Ans:
   (2) Clark's method

43) Which one is malachite from the following?
  (1) CuFeS
 (2) Cu(OH)
 (3) FeO
 (4) CuCO.Cu(OH)

Ans.:  
 (4) CuCO.Cu(OH) 
    Chalcopyrite or iron pyrite (CuFeS₂) & magnetite (FeO).

44) The correct order of the basic strength of methyl substituted amines in aqueous 
      solution is: 
  (1) (CH)NH > CHNH> (CH)N
  (2) (CH)N > CHNH>  (CH)NH
  (3) (CH)N > (CH)NH >  CHNH
  (4) CHNH > (CH)NH >  (CH)N


Ans.:
     (1) (CH)NH > CHNH> (CH)N
   
The correct order of the basic strength of methyl substituted amines in aqueous solution is: