Geminale Substituenteneffekte, 4. Abhängigkeit des inversen anomeren Effektes geminaler Nitril‐Gruppen von der Struktur

Abstract

Geminal Substituent Effects, 4. — The Dependence of the Inverse Anomeric Effect of Geminal Cyano Groups on the Structure The heats of combustion and the heats of sublimation of malodinitrile (1a), ä‐alkyl‐ (1b,c) and å, å‐dialkylmalodinitriles (1 d ‐f) have been determined. From the obtained standard heats of formation group increments for CH2[CN]2], CH[(CN)2 Cl and C[CN)2C2] group are deduced. The comparison of their values with corresponding increments for monocyano alkanes reveals a synergetic destabilisation by two geminal cyano substituents of 11.5, 9.0 and 6.6 kcal/mol, respectively. Thus, this inverse anomeric effect decreases by increasing alkyl substitution.

Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy”

“…These confirm that malononitrile and butane-dinitrile are distinct cases, and higher species follow the formula Equation (15b). This is supported by Beckhaus et al [27], who reported, in a paper on geminal substituent effects, a synergetic destabilization by two geminal cyano substituents of 11.5 kcal/mol or 48 kJ/mol. In their paper, they also evaluated the heat of formation and found 266.5 kJ/mol for malononitrile, in good agreement with the NIST value in Table 5.…”

“…Thus, malononitrile is considered a regular molecule for which the heat of formation is purely additive with first-order contributions, namely, for CH 2 CN and CN only. Based on the energy differences between successive species in the series, and our ab initio and DFT calculations and the work by Beckhaus et al [27], we have to conclude that the MG ICAS23 results are not based on the correct chemistry.…”

“…Table 5. Results for substituted malononitriles, where predictions from the currently proposed model are compared to experimental results obtained from [27]. The results, in particular, the difference between the model and experiment, reflect the statement made in [27] that the deviation is dependent on the degree of substitution.…”

“…For alkylsubstituted malononitriles, this effect decreases with increasing substitution but is still present, viz., Table 5. Thus, the alkylsubstituted malonitriles need to be treated separately which we will not further discuss here, but [27] provides the first useful data to push this forward.…”

Thermochemical study of aliphatic and phenyl-substituted geminal diacetates

“…As a result it was shown that electron donating substituents like alkoxy groups (in acetals [2,11] and ortoesters [7]) or amino groups (in aminales [8]) experience synergetic stabilization, generally called "anomeric stabilization," which is mainly caused by 7r-a* conjugation (a through bond effect). On the contrary, combinations of electron-withdrawing substituents (CN, COOR, COR) show a destabilizing synergetic effect [1,5,9,13] mainly caused by repulsive interaction through space. We turn our attention in this publication to the geminaI interaction of .…”