The present thesis consists of two parts, Part A deals with the isolation of natural products. Plants are being used as medicine since the beginning of human civilization, perhaps as early as origin of man. Healing powers are reported to be present in plants and therefore it is assumed that they have medicinal properties. The present Ph. D thesis deals with isolation of bioactive constituents from medicinally important plant of Pakistan namely Vernonia oligocephala. Part B deals with green solvents (ILs) and their chemistry. Mixtures of ionic liquids, ILs, and molecular solvents are used because of practical advantages. Solvation by mixture of solvents is, however, complex because of preferential solvation.