The heats of combustion of nitromethane, nitroethane, l-nitropropane, 2-nitropropane, dimethylnitramine, and diethylnitramine have been measured. The group-energy terms for the (C-NO,) and (N-NO,) groups are derived from these data and that for ) from published data. The significance of the results is considered.ANALYSIS of the molecular energetics (mean bond-and resonance-energy terms) for the X-NO, system, where X = R3C, R,N, and RO, is of general interest and particularly desirable in view of the practical importance of thermal data on such compounds. The analysis is complicated by (i) the simultaneous occurrence of formal charge and resonance effects within the grouping (I), (ii) uncertainties in the values of the mean bond-energy terms for the bonds N-0 and "0, and (iii) the probability, when X = R,N or RO, of additional mesomerism involving the excited structures (11) and (111). We have therefore approached the analysis in stages, evaluating first, from heats of combustion and latent (1) (IV) (V)heats, the '' group-energy term " for each of the three types of X-NO, group, E(C-NO,), E(N-NO,), and E(0-NO,). The group-energy term is the enthalpy change, -A H , for the hypothetical gas-phase formation of the nitro-group, e.g., E(C-NO,) is -A H for R3C* + N + 2 0 _t R,C-NO,, i.e., the group energy is that part of the atomic heat of formation, -AH,, a, of the nitro-compound corresponding to the actual formation and attachment of the nitro-group, and includes formal charge and resonance effects, mean bond-energy terms, and any additional mesomeric effects. These group-energy terms can be used directly in the evaluation of -AH,, a terms for hypothetical nitro-compounds of all three classes.We have attempted to carry the analysis a stage further and to disentangle the various components of the group-energy terms. EXPERIMENTAL MateriaZs.-Benzoic acid. The B.D.H. thermochemical standard product ( -A Vt, = 6.3181 f 0.0007 kcal.1g.i) was used. Nitroalkanes. These (I.C.I.) were each distilled through an 18 in. column packed with glass helices. Fractions collected were : nitromethane, b. p. 99.7-99.9"/750 mm. (lit.,l
The heats of combustion of o-dimethoxybenzene, 1 : 3-dioxaindane, 1 : 4dioxatetralin, and 2 : 3-benzo-1 : 4-dioxacycloheptane have been measured. The resonance energies are derived and are discussed in terms of the structures of the non-aromatic groupings. EXPERIMENTALMaterials.-o-Dimethoxybenzene (from Messrs. Hopkin and Williams) was distilled through The fraction collected had b. p. 205.5"/748 mm. Heilbron and Bunbury l a 6" Fenske column. give b. p. 206'1759 mm. from methylene sulphate and o-dihydroxybenzene. Distilled through an 18" Fenske column, the fraction collected had b. p. 173.2-173.5O/758 mm. Baker gives b. p. 173-174'1756 mm. 1 : 4-Dioxatetralin (2 : 3-dihydrobenzo-1 : 4-dioxan) was prepared from ethylene bromide and o-dihydroxybenzene in the presence of potassium carbonate, copper bronze, and glycer01.~ It distilled at 213-2'/774 mm. Gattermann3 gives b. p. 206--207'/749 mm.2 : 3-Benzo-1 : 4-dioxacycloheptene (6 : 7-dihydro-2 : 3-benzo-1 : 4-dioxepin) was prepared by heating o-dihydroxybenzene (27.5 g . ) , 1 : 3-dibromopropane (50 g.), finely powdered anhydrous potassium carbonate (35 g.), glycerol (1 g.), and copper bronze (1 g.) under reflux for 10 hr.4 The mixture was cooled, diluted with water (30 ml.), and made faintly alkaline with sodium hydroxide, then steam-distilled, and the distillate was extracted with chloroform. The chloroform layer was separated, dried (Na,SO,), and distilled. The product was distilled through a 6" Fenske column, the fraction collected having b. p. 100.5"/11 mm (Found: C,
Complexes of PhenyIdialky2-phosp~~iites and -arsines. 4007Metal Complexes formed by Some Substituted Phenyldialkylphsphines and -arsines.
Let $G$ be a split connected reductive group over a finite field of characteristic $p > 2$ such that $G_\text {der}$ is absolutely almost simple. We give a geometric construction of perverse $\mathbb {F}_p$ -sheaves on the Iwahori affine flag variety of $G$ which are central with respect to the convolution product. We deduce an explicit formula for an isomorphism from the spherical mod $p$ Hecke algebra to the center of the Iwahori mod $p$ Hecke algebra. We also give a formula for the central integral Bernstein elements in the Iwahori mod $p$ Hecke algebra. To accomplish these goals we construct a nearby cycles functor for perverse $\mathbb {F}_p$ -sheaves and we use Frobenius splitting techniques to prove some properties of this functor. We also prove that certain equal characteristic analogues of local models of Shimura varieties are strongly $F$ -regular, and hence they are $F$ -rational and have pseudo-rational singularities.
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