--%>
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 : Explain solid in liquid solutions. The

    The French chemist Francois Marie Raoult (1886) carried out a series of experiments to study the vapour pressure of a number of binary solutions. On the basis of the results of the experiments, he proposed a generalization called Raoult's law which states that, <

    		•
  • Q : Explain Solid Compound Formation. In

    In some two component, solid liquid systems, a solid compound forms.In systems in which the components have an interaction for such other, a solid state compound of the two compounds of the two components can form.Formic acid and formaide form a solid state, one-to-one com

    		•
  • Q : Vapour pressure of volatile substance

    Provide solution of this question. According to Raoult's law the relative lowering of vapour pressure of a solution of volatile substance is equal to: (a) Mole fraction of the solvent (b) Mole fraction of the solute (c) Weight percentage of a solute (d) Weight perc

    		•
  • Q : Electrons present in a benzene How

    How many electrons are present in a benzene?

    		•
  • Q : Homework Silicon has three naturally

    Silicon has three naturally occurring isotopes. 28Si, mass = 27.976927; 29Si, mass = 28.976495; 30Si, mass = 29.973770 and 3.10% abundance. What is the abundance of 28Si?

    		•
  • Q : Rotational energy and entropy due to

    The entropy due to the rotational motion of the molecules of a gas can be calculated. Linear molecules: as was pointed out, any rotating molecule has a set of allowed rotational energies. For a linear molecule the

    		•
  • Q : Explain reactions of carbonyl oxygen

    In these reaction oxygen atom of carbonyl group is replaced by either one divalent group or two monovalent groups. Reaction by ammonia derivatives: aldehydes and ketones react with a number of ammonia derivatives such as hydroxylaminem hydrazine, semicarbazide etc. in weak acidic medium.

    		•
  • Q : Law of multiple proportions and Law of

    Describe the difference between law of multiple proportions and law of definite proportions?

    		•
  • Q : Vapour pressure over mercury Choose the

    Choose the right answer from following. At 300 K, when a solute is added to a solvent its vapour pressure over the mercury reduces from 50 mm to 45 mm. The value of mole fraction of solute will be: (a)0.005 (b)0.010 (c)0.100 (d)0.900

    		•
  • Q : Organic and inorganic substances living

    living beings are made up of organic and inorganic substances.according to their complexity of their molecules how can ach of these substances be classified?

    		•