Binary mixtures of nematic 4-pentyl-4′-cyanobiphenyl (5CB) with some kinds of non-nematic solutes were found to show the increase in nematic-isotropic transition temperature, contrary to usually observed decrease. All these ‘unusual’ solutes found in this work have active hydrogen atoms which can act as hydrogen bond donor. ‘Unusual’ increase in the clearing temperature was attributed to the hydrogen bonding interaction between 5CB and solutes. The effect of hydrogen bonding interaction between 5CB and various non-nematic solutes on thermal and spectroscopic properties were studied in detail.