Determining a Molecular Formula Mesitylene, a hydrocarbon found in crude oil, has an empirical formula of C3H4 and an experimentally determined molecular weight of 121 amu. What is its molecular formula? Cyclohexane, a commonly used organic solvent, is 85.6% C and 14.4% H by mass with a molar mass of 84.2 g/mol. What is its molecular formula? (a) C6H (b) CH2 (c) C5H24 (d) C6H12 (e) C4H8.
Answer: Step 1 Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemi melitene). All three compounds have the formula C H (CH 6 3whic3 3commonly abbreviated C H Me . Mesityle6 3 3 is a colourless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C H Me and is found in various other compounds. 6 2 3