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Tuesday, February 4, 2020

How to calculate radius ratio triangular voids?

The triangular voids are found in the planes of the close packed structures, whenever three spheres are in contact in such a fashion. Coordination number of triangular void is three. Here three atoms A, B, and C form triangular voids in which equilateral triangle form having angle 600

WhereR= Radius of the (Atoms) sphere= maximum radius of a sphere that can be placed inside the void or radius of void.

Why transition metals and their compounds are act as catalyst?

Transition metals and their compounds are known to act as good catalyst due to the following reasons: 
(1) Due to the variable oxidation state, they form unstable intermediate compounds and provide a new path with lower activation energy for the reaction (Intermediate compound formation theory) and hence rate of reaction is increases.
(2) In some cases the finely divided metals or their compounds provide a large surface area for adsorption and the adsorbed reactants react faster due to the closer contact (Adsorption theory).
Some Important Catalytic:
1. TiCl3 + Al(C2H5)3 Used as Ziegler – Natta catalyst 
2. V2O5 Converts SO2 to SO3 in the contact process for making H2SO4
3. MnO2 Used as a catalyst to decompose KClO3 to give O2
4. Fe Used in Haber – Bosch process for making NH3
5. FeCl3 Production of CCl4 from CS2 and Cl2
6. FeSO4 & H2O2 Fenton's reagent 
7. PdCl2 Wacker process for the following conversion 
            C2H2 + H2O + PdCl2 to CH3CHO + 2HCl + Pd 
8. Pd For hydrogenation (Phenol to Cyclohexanol) 
9. Pt/PtO Adam catalyst used for reduction 
10. Pt SO2 to SO3 contact process 
11. Pt Cleaning car exhaust fumes 
12. Cu In manufacture of (CH3)2SiCl2
13. Cu/V Oxidation of cyclohexanol 
14. CuCl2 Deacon process or making Cl2 from HCl 
15. Ni Raney nickel
16. Pt/Rh Ostwald's process. NH3 to NO
17. Baeyer's reagent - 1% alkaline solution of KMnO4.
18. Etard's reagent- CrO2Cl2 Chromyl chloride.
19. Luca's reagent- Anhydrous ZnCl2+ concentrated HCl.
20. Barford reagent- Cu(CH3COOH)2+ CH3COOH.
21. Brown catalyst- Nickel Boride.
22. Lindlar's Catalyst- Pd/C use to convert alkynes to cis alkenes.
23. Adkin's catalyst- (CuO.CuCr2O4) or CuO.Cuo.Cr2O3, Copper chromite is use to reduce corboxylic acids into corresponding alcohols 

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Monday, February 3, 2020

How is base strength related to the availabihty of the electron-pair?

Base strength depends on the ability of the basic site (which always has an unshared electron pair) to accept a proton. This ability depends on the charge in an anion or electron density in a molecular base. For species with an identical charge, dispersal or delocalization of the electrons from the basic site to other parts of the molecule results in decreased electron density and decreased base strength.

Related Questions:
  1. What is relative basic strength order 1° amines , 2°amines and 3° amines ? 
  2. Explain:Arrange the following in the increasing order of their acid strength : Methyl amine, Dimethyl amine, Aniline, N-methyl aniline (I.I.T, 1988).
  3. What is Carbylamine test or Isocyanide test ?
  4. What is Hinsberg's reagent and where Hinsberg's test use?
  5. Can we prepare aniline by Gabriel – phthalimide reaction?
  6. N-Ethyl-N-methyl propanamine does not show optical activity why?
  7. What is relative basic strength order 1° amines , 2°amines and 3° amines ? Explain:
  8. Amines are more basic than ammonia why?
  9. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
  10. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
  11. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
  12. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
  13. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
  14. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
  15. Why pyridine is more basic than Pyrrole?
  16. Why pyrimidine is less basic than pyridine?
  17. Imidazole is more basic than pyridine? Why?
  18. Biological Important of Imidazole and structure:
  19. Pyridine is almost 1 million times less basic than piperidine? Why?
  20. Cyclohexylamine amine is the stronger base than Aniline? Why?
  21. Tetrahydroquinoline amine is the stronger base than Tetrahydroisoquinoline? Why?

Alcohols and Phenols both are acidic but phenols are more acidic. Why?

Alcohols and phenols both are acidic in nature because they Liberate H2 with active metals. But alcohols are weaker acids than phenols because,  
(i) Alcohols fail to turn blue litmus red:
(ii) Alcohols fail to neutralize alkalies whereas phenols do so:
(1) Both phenol and phenoxide ions exhibit resonance, whereas alcohols and alkoxide ion do not.
(2) Due to resonance, positive charge 's developed over "O" of phenol this weakens O-H bond and facilitates release of a proton. On the other hand due to electron donating nature of alkyl group -O-H bond is strengthened. Therefore it hinders the release of proton.      
(3) The phenoxide ion is more stable than phenol, due to greater dispersal of negative charge, therefore. Equilibrium get shifted to forward direction. whereas alkoxide ion is less stable than alcohols due to intensification of negative charge, so equilibrium get shifted towards backward direction. Hence phenols are more acidic than alcohols. 

Related Questions:

Phenoxide ion is more stable than an alkaoxide. why?

Sunday, February 2, 2020

CCl4 can not be hydrolysed but SiCl4 can be. Why?

Carbon tetrachloride (SiCl4) easily hydrolysed due to availability of vacant d – orbitals in valence shell of their central atom ( Silicon), hence it can easily extend their coordination number beyond four but this is not possible in case of carbon tetrachloride (CCl4) due to absence of vacant d – orbitals in carbon atom.

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