--%>
Assignment Help - homework help

What is ortho effect?

Orthosubstituted anilines are generally weaker bases than aniline irrespective of the electron releasing or electron withdrawing nature of the substituent. This is known as ortho effect and may probably be due to combined electronic and steric factors.

The overall basic strength of ortho, meta and para substituted anilines, however, depends upon the electron,-donatingelectron-withdrawing resonance effect as well as inductive effect as discussed below:

(a) If the substituent has electron withdrawing inductive (-I) as well as resonance (-R) effect. Then all the substituted anilines are weaker bases with ortho isomer being the weaker base. Then m-isomer in this case is relatively stronger base because R-effect does not operate at m-positive. For example, basic strength of o, p, m-nitro anilines are given as follows:

(b) If the substituent has electron donating inductive (+I) as well as electron donating resonance (+R) effect, then among the substituted anilines, the ortho substituted anilines are weaker bases than aniline whereas p- and m- isomers are relatively stronger bases. However, the p-isomer is still stronger than m-isomers. This is clear from the basic strength of toluidines as given below:

(c) If a substituent has electron donating resonance effect (+R) but electron withdrawing inductive effect (-I), the overall basic strength depends upon the relative predominance of R-effect or I-effect.

(i) When a substituent has strong (+R) effect and weak (-I) effect (For example, -OCH3 group). At meta-position it exerts only (-I) effect causing base weakening effect. Among o- and p-isomers, ortho isomer is weaker base than aniline due to ortho effect while para-isomer is stronger base than aniline due to dominance of + R effect. The basic strength of o-, p- and m-anisidines are as under:

Similar trends are observed in amino-phenols with any ortho aminophenol is stronger base than aniline due to stabilization of o-hydroxy anilinium ion because of intramolecular H-bonding. The basic strengths of aminophenols are as under:

-NH2 group has much stronger (+R) effect and much weaker (-I) effect than -OH group and -OCH3 groups. The decreasing order of basic strengths of phenylenediamines is as given below:

(ii) when the substituent has a weak +R effect but a strong -I effect Chloro group (-Cl) is common example. Since -I- effect outweighs the +R effect, therefore, all the three o-, m- and p- chloroanilines are weaker bases than aniline. However, due to ortho-effect, o-chloroaniline is the weakest base. Further in p-chloroaniline is the weakest base. Further in p-chloroaniline both +R only the -I effect operates; therefore, p-chloroaniline is relatively stronger base than m-chloroaniline. Thus, the basicity of o-, m- and p- chloroanilines relative to aniline follows the sequence as given below:

   Related Questions in Chemistry

  • Q : What are homogenous catalyst? Give few

    When a catalyst mixes homogeneously with the reactants and forms a single phase, the catalyst is said to be homogeneous and this type of catalysis is called homogeneous catalysis. Some more examples of homogeneous catalysis are:    SO2

    		•
  • Q : Electrons present in a benzene How

    How many electrons are present in a benzene?

    		•
  • Q : Molarity of Nacl solution When 5.85 g

    When 5.85 g of NaCl (having molecular weight 58.5) is dissolved in water and the solution is prepared to 0.5 litres, the molarity of the solution is: (i) 0.2 (ii) 0.4 (iii) 1.0 (iv) 0.1

    		•
  • Q : Relationship between free energy and

    The free energy of a gas depends on the pressure that confines the gas. The standard free energies of formation, like those allow predictions to be made of the possibility of a reaction at 25°C for each reagent at 

    		•
  • Q : Group Cations Explain how dissolving

    Explain how dissolving the Group IV carbonate precipitate with 6M CH3COOH, followed by the addition of extra acetic acid, establishes a buffer with a pH of approximately

    		•
  • Q : Problem based on molarity Select the

    Select the right answer of the question. If 18 gm of glucose (C6H12O6) is present in 1000 gm of an aqueous solution of glucose, it is said to be: (a)1 molal (b)1.1 molal (c)0.5 molal (d)0.1 molal

    		•
  • Q : Problems related to entropy change A)

    A) Two compartments each of 1 m3 capacity are joined by a valve and insulated from the surroundings and from one another. One compartment has saturated steam at 683.6 kPa and the other contains steam at the same temperature but at a pressure of 101.3 kPa. T

    		•
  • Q : Molar solution of sulphuric acid Choose

    Choose the right answer from following. The molar solution of sulphuric acid is equal to: (a) N solution (b) 2Nsolution (c) N/2solution (d) 3Nsolution

    		•
  • Q : Solution density of water is 1g/mL.The

    density of water is 1g/mL.The concentration of water in mol/litre is

    		•
  • Q : Inorganic Chemistry Inorganic

    Inorganic Chemistry:In the year 1869, Russian Chemist Dmitry Mendeleyev forms the periodic table of the element. Since Newlands did before him in the year 1863, Mendeleyev categorizes the el

    		•