Organic Chemistry Lab Report

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Excess molar volumes were measured at 308.15K as a function of composition by a direct dilatometer method for binary liquid mixtures of 4-methylpentan-2-ol + n-hexane, + n-heptane, + n-octane, + n-decane and + n-dodecane. All the mixtures exhibit positive excess volumes over the whole mole fraction range. VE results of 4-Methylpentan-2-ol with n-alkanes were compared with VE of Hexanol-1 + n-alkanes. The variation of VE with the change in the position of either alkyl group or –OH group is discussed.

1. Introduction
The molar excess volumes of binary liquid mixtures particularly alkanol – alkanes mixtures have been determined by many workers (Kaur et al.,1989, 1991and Mahajan et al.,2013) and the results have been utilized to check the validity
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Kaur,1985) which give sigmoid shape with (n-hexane, n-heptane and n-decane), i.e. show both negative and positive values at low and high mole fraction range. This can be explained as consequence of two opposing effects, the disruption of H-bonded alcohol aggregates by alkane molecules contribute negative VE whereas change in free volume and interstitial accommodation of smaller alkane molecules into the alkanol structure give negative contribution. The latter effect gets stoically hindered in 4-methylpentan-2-ol due to positive contribution due and is dominated by the positive contribute due to disruption of H-bonds. Self association due to H-bonds also become weaker due to steric hindrance to H-bond formation in 4-methylpentan-2-ol as compared to Hexan-1-ol which cause more positive VE values for 4-methylpentan-2-ol. The shape of the molecule is another factor which contributes more positive value of VE to 4-methylpentan-2-ol. The Hexan-1-ol molecule is planer and elongated in same fashion as those of n-alkanes. The alignment of these molecules on mixing is ordered due to Vander Waal’s forces. The 4- methylpentan-2-ol molecules are bulky and spherical in shape. The alignment on mixing is likely to be random. These molecules may also destroy the ordered alignment of n-alkane

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