Steric effects on the self-association of branched and cyclic alcohols in inert solvents. Apparent heat capacities of secondary and tertiary alcohols in hydrocarbons

Abstract

Chem. 66,989 (1988).Apparent heat capacities have been measured for fifteen branched and cyclic alcohols in dilute n-decane solution at 25OC. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-methyl-3-pentanol, trans-, cis-, and mixed isomer 2-methylcyclohexanol, I-methylcyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 3,7-dimethyl-I-octanol, 5-decanol, 4-propyl-4-heptanol, cyclododecanol, 5-butyl-5-nonanol, and 8-hexadecanol (in n-hexane). Excess heat capacities cPE throughout the concentration range were measured at 25OC for: 1-hexanol + n-hexadecane (11-CI6) and + 2,2,4,4,6,8,8-heptamethylnonane (br-C16), 4-propyl-4-heptanol, and 1-decanol + n-decane, 3-methyl-3-pentanol + 11-c~~ and + br-C16 and at 27OC for cyclohexanol + 1 1 -c~~ and + br-CI6 Also, for 3-methyl-3-pentanol + n-decane CpE was measured at 10, 25, 40, and 50°C. For a series of isomeric alcohols, the apparent molar heat capacities show a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the alcohol becomes increasingly hindered, effectively reducing the alcohol self-association capabilities. This situation is also reflected by the heat capacities of the pure alcohols which increase strongly in magnitude in going from a linear I-alcohol to an isomeric alcohol which has its hydroxyl group on a quaternary carbon atom. cPE of the mixtures are negative at low alcohol concentrations turning positive at increasingly higher alcohol concentrations as the steric hindrance on the hydroxyl group increases. Throughout most of the concentration range cPE for the branched or cyclic alcohols is considerably more positive than for the corresponding isomeric 1-alcohol. For the highly hindered 3-methyl-3-pentanol c P E (~) passes through a maximum. All of the above behaviour is explained by the Treszczanowicz -Kehiaian model for self-associated liquids + inert solvents which has been applied to the present data. Equilibrium constants have been obtained for alcohol association and are sensitive to alcohol structure. At low alcohol concentrations, while for the linear I -alcohols tetramers are the predominant species and dimer are almost absent, for the corresponding isomeric alcohols the concentration of tetramers is severely reduced and the lower species, i.e. trimers and dimers, are more important. For the highly hindered alcohols, monomers are the predominant species in dilute solution reflecting the decrease in self-association ability that steric hindrance of the hydroxyl group imposes on them.MERCEDES CACERES-ALONSO, MIGUEL COSTAS, LINA ANDREOLI-BALL et DONALD PATTERSON. Can. J. Chem. 66, 989 (1988).OpCrant i 25"C, on a mesure les capacitis calorifiques apparentes de quinze alcools ramifiCs et cycliques en solutions diluCes dans le n-dCcane. I1 s'agit des alcools suivants : methyl-2 propanol-2, cyclohexanol, methyl-3 pentanol-3, les isomtres cis-et trans-du mCthyl-2 cyclohexanol, methyl-l cyclohexanol, Cthyl-3 pentanol-3, cyclooctanol, dimethyl-3,7 octanol-1, dCcanol-5, propyl-4 heptanol-4,...

Calculation of the Isobaric Heat Capacities of the Liquid and Solid Phase of Organic Compounds at and around 298.15 K Based on Their “True” Molecular Volume

“…Beyond these compilations a large number of recent papers presenting the heat-capacity data of several classes of compounds and of individual molecules of any kind as well as their temperature dependence have been published up to the present. Special mention shall be given to the hydrocarbons [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65], halogenated hydrocarbons [66,67,68,69,70,71], unsubstituted and substituted alcohols and polyols including sugar derivatives [72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107], phenol derivatives [108,109], carboxylic acids […”

Molar heat capacities for (2-methyl-2-butanol+heptane) mixtures and cyclopentanol at temperatures from (284 to 353)K

“…The heat capacity of (alcohol + alkane) mixtures is useful for the understanding of the self-association of alcohol molecules in solutions [7,[9][10][11][12][13][14][15][16]. Mixtures of alkanols with alkanes are liquid systems most frequently studied under atmospheric pressure.…”

Excess isobaric molar heat capacities and excess molar volumes for ethanol+n-decane and n-undecane systems

“…1-Alkanol + alkane systems were extensively analyzed from theoretical and experimental points of view [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Their thermodynamic behavior is characterized by a strong departure from ideality, fact reflected in the high values of their excess properties, specifically, of their excess isobaric molar heat capacities.…”