Benzoic acid and their derivatives like salicylates are important compound with wide biological, pharmaceutical and industrial applications. These are used as anti inflammatory and disinfectant drug in the pharmaceutical applications. The acetylation of amines, alcohols and phenols is an important chemical reaction in organic synthesis. Part one of this work is the synthesis of several derivatives of these compounds. The friedel-crafts acylation of aromatic compounds is the important reaction for the synthesis of aromatic ketones, which are useful intermediates in the chemical industry. Reaction of methoxy benzene and ortho anisidine was used with chloroformate and acetic anhydride acylating reagent with or without present ionic liquid (IL). The development of heterogeneous catalysts like IL has played an important role, since they offer advantages such as clean reaction conditions, easy separation of the catalyst from the reaction medium, greater selectivity and generally give higher yield of products and can be recycled for a number of times. First methylation of rich arene, anisole with mild reagent, chloroformate and green ionic liquid catalyst, 3-carboxy-piridinium hydrogen sulphate( 26 ) was done to produce selective products such as 2-methyl-methoxy benzene( 37 ) and 4-methyl-methoxy benzene( 38 ). Then acylation of ortho anisidine with acylating reagent acetic acid to produce ortho anisidide( 28 ) and 2-methoxy-5-acetyl acetanilide( 29 ) was done. Also methyl formation of ortho anisidine with chloroformate to produce methyl-2-methoxy-phenyl carbamate( 30 ) was done. Also the use of appropriate catalyst, role, kind and amount of it has been investigated because of importance of green chemistry. Optimized condition in term of reaction time and temperature was studied. Catalyst as aluminium tri chloride, alumina, ionic liquid (3-Carboxy-piridinium hydrogen sulphate) and montmorilonite-k10 (activated with hydrochloric acid or sulfuric acid) were used. The synthesized compounds were characterized by elemental analysis, GC/MS, 1 H-NMR, 13 C-NMR and FT-IR. In theoretical part of this project, the effect of intramolecular hydrogen bonding, hyper conjugation and steric effect on [di-amino ( 31 ), di-nitro ( 32 ) and amino-nitro ( 33 )] ethane were studied by performing HF, DFT and MP2 levels of theory using 6-311++G** basis set. The total energy, relative energy and optimized geometries were calculated. The length of hydrogen bonding and length of C 1 -C 2 bond for studying the intensity of the hydrogen bonding and hyper conjugation of all conformers for each compound were compared relatively. The conformational analysis was done for these derivatives of ethane to find the energy minima and maxima conformers.