Diethyl ether enthalpies

Self-Tfst 7.7B Use Trouton s rule to estimate the standard enthalpy of vaporization of diethyl ether, C4H1()0, which boils at 34.5°C. 

Beak and Siegel studied the protodelithiation of the lithioanisole isomers by ethanol in di-n-butyl ether solution. As are phenyl lithium in diethyl ether solution and o-lithioanisole in dibutyl ether solution, the p- and m-lithioanisoles also were presumed to be predominately dimeric in the di-n-butyl ether solution. As dimers, the o-isomer is some 35 kJ mop more stable than the nearly isoenergetic m- and p-isomers, consistent with intramolecular association between the lithium and oxygen. That the inductive effect is small in comparison with association is shown by the nearly identical enthalpies of protodelithiation of the p- and m-lithioanisoles. 

Thermochemically, the association is not a major factor since the enthalpies of dilution of Grignard reagents are very small in diethyl ether as well as in THF An explanation... 

Holm determined the enthalpies of formation of a collection of hydrocarbyhnagnesium bromides by reaction calorimetry with HBr in diethyl ether . He also determined the enthalpies of formation in ethereal solution of the magnesium bromide salts of 20 Bronsted acids, HB, by measuring the enthalpies of reaction of the acid with pentylmag-nesium bromide. For those species that were reported in both studies (hydrocarbyl = phenylethynyl, phenyl, methyl, cyclopropyl, cyclopentyl, cyclohexyl), the enthalpies of formation were identical. The values are listed in Tables 3 and 4. 

Quantum-chemical (DFT, B3LYP/6-31G") calculations have been performed to determine the relative stabilities of the tautomer pairs 69/70 (gas-phase reaction enthalpy calculated 1.2 kcal mol , experimental value in diethyl ether 1.1 0.1 kcalmol ), 71/72 (gas-phase reaction enthalpy calculated 2.1 kcal mol ), and 73/74 (gas-phase reaction enthalpy calculated 2.6kcalmol , experimental value in dipentyl ether 1.9 0.1 kcal mol ). In all cases, the tautomer with the endo C=C bond is strongly favored over the one with the exo C=C bond. Because of the overwhelming stability of 2,5-dimethylfuran versus tetrahydro-2,5-bismethylenefuran 71 and 2,3-dihydro-5-methyl-2-methylenefuran 72, the equilibrium 71 72 cannot be observed experimentally <2001STC405>. ... 

Table IV. Enthalpy Changes (kcal mol-1) for Reactions between Water, Diethyl Ether, and Acids (HA) and Ions (T)...

Using the plots in Fig. 16.48(b), determine whether water or diethyl ether has the smaller enthalpy of vaporization. 

Note from Fig. 16.48(b) that the slopes of the lines for water and diethyl ether are both negative, as expected. Also note that the line for ether has the smaller slope. Thus ether has the smaller value of AHvap. This makes sense because the hydrogen bonding in water causes it to have a relatively large enthalpy of vaporization. 

Of these, probably the most decisive are type 2 and the combination of types 1 and 3. It is difficult to rationalize the weak H bonds formed by acetonitrile as a base (molecular dipole moment of 3.44 d) and the strong H bonds formed by trimethylamine (molecular dipole moment of 0.7 d) together with the interpretation that an acid A—H forms H bonds with these bases because of the electrostatic interaction of the A—H dipole with point charges on the nitrogen atoms. Another interesting comparison is afforded by the approximately equal H bond properties of acetone, diethyl ether, and dioxane, with dipole moments of 2.85 D, 1.15 D, and 0.4 d, respectively. These qualitative discrepancies can be backed by a substantial body of quantitative data. Table 8-1 collects some of these data, and verifies the absence of any systematic dependence of enthalpy of H bond formation upon the molecular dipole moment. Compilations of At, (814) and of AFshow that these properties are similarly unrelated to /i- Certainly these data show that the strength and behavior of a H bond are not determined in a direct way by the dipole moment. This lack of dependence is not easily reconciled with... 

Calculate the enthalpy of adduct formation predicted by Drago s E, C equation for the reactions of I2 with diethyl ether and diethyl sulfide. 

The molar heat capacity of diethyl ether, (C2H5)20(/), is 172 J/K mol. What is the temperature change if the molar enthalpy change equals -186.9 J/mol ... 

A number of diethyl ether-dihalogenoalane adducts have been prepared and characterized by X-ray powder diffraction studies. The standard enthalpy of formation of HAlCl2,OEt2 was calculated to be — 774.29 kJ... 

Metal-silicon bond disruption enthalpies have been measured for a series of metallocene complexes including Gp3USi(SiMe3)3. This complex was synthesized by reaction of Cp3UCl with LiSi(SiMe3)3(THF)3 in diethyl ether. The thermodynamic data were obtained by titration calorimetry with I2 (Scheme 29).80... 

Table 1 1- Enthalpies nl formation ni ulkyltnuguesiinn bromides dissolved in diethyl ether and lliermiicheinival bond dissociation energies lor the C -Me httnd...

Table l.l. Enthalpies of Idrnialion of alkylmagncsiunt hromidcs dissolved in diethyl ether and thermocheniical bond dissociation energies for the C—Me bond... 

It is of interest to note that Kminek, Kaspar and Trekoval have made calorimetric measurements on the interaction of n-butyllithium with several Lewis bases at RLi/base ratios of one. The largest enthalpy changes (in agreement which the results of Quirk and Kester were found for TMEDA and dimethoxyethane and the smallest with diethyl ether and anisole. Their results for anisole clearly show that even aromatic ethers will interact and complex with organolithium species. Thus, their findings serve to fortify the viscometric findings regarding the influence of aromatic ethers on the poly(styryl)lithium association state. 

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