Substituenteneffekte auf die CC‐Bindungsstärke, 1. Struktur und Spannungsenthalpie tetrasubstituierter Bernsteinsäuredinitrile

Abstract

Substituent Effects on the C-C-Bond Strength, 1 Structure and Strain Enthalpy of Tetrasubstituted Succinonitriles')Eleven Succinonitriles, tetrasubstituted by alkyl or aryl groups, were prepared, partially as pure meso-and DL-diastereomers. For four of them standard heats of formation AH; and strain enthalpies Hsp were determined from heats of combustion. Their values were used together with data from the literature to deduce the CN-base value required for the computation of heats of formation AH; of nitriles and dinitriles with Allinger's MM2 force field. In addition rotational barriers, conformational equilibria, dipole moments and structures were determined by force field calculations. The agreement with experimental data as e.g. the X-ray structures of 7d und 7g was good. The relationships between strain and structure are discussed.In einer Reihe von Publikationenz-') haben wir gezeigt, da0 zwischen der Struktur, der Spannungsenthalpie und der thermischen Stabilitat hochverzweigter Kohlenwasserstoffe eindeutige Beziehungen bestehen. Mit der Verzweigung der Seitenketten R' -R3 in 1 steigt deren Spannungsenthalpie Hsp 697), die experimentell durch Verbrennungskalorimetrie3) oder rechnerisch durch Kraftfeldrechnungen3s8) bestimmt werden kann, an. Linear parallel mit der Spannungsenthalpie H s p sinkt die Aktivierungsenthalpie (AG" bzw. AH*) des homolytischen Zerfalls in die Radikale 22,4). Beriicksichtigt man die in den Radikalen 2 verbleibende Restspannung ' ), die durch Kraftfeldrechnungen 0 Verlag

3,4‐Dihydro‐3H‐pyrrol‐2‐imines as Conformationally Restrained 1,3‐Diazabutadienes: Synthesis, Structural Properties and Protonation

“…The procedure for the synthesis of the N ‐silylated 5‐aryldihydropyrrol‐2‐imines was adapted from the protocol used by Marihart, Greving et al to synthesise conformationally restrained 1,3,5‐triazapenta‐1,3‐diene building blocks for oligonitriles,12which in turn is based on a procedure published by Wöhrle 11. The employed 2,2,3,3‐tetramethylsuccinonitrile ( 1 ) is easily available by controlled decomposition of azoisobutyronitrile (AIBN) 13. This tetramethyl‐substituted dinitrile is nonenolisable, which is advantageous for the reactions reported here.…”

Synthesis, Spectroscopic, and Electrochemical Studies of 1,2‐Naphthalene‐Ring‐Fused Tetraazachlorins, ‐bacteriochlorins, and ‐isobacteriochlorins: The Separation and Characterization of Structural Isomers

“…[27] 4-Phenyl-1,2-naphthalenedicarboxylic anhydride (24) was also obtained by the method described in the literature [28] by condensation of 1,1-diphenylethylene (22) with maleic anhydride (18), followed by dehydrogenation of the resulting bis-adduct (23) using sulfur. 1,2-Naphthalenedicarboxylic imide (26) was obtained as previously described [28] by heating 1,2-naphthalenedicarboxylic anhydride (19) with urea.…”

Synthesis and Spectroscopic and Electrochemical Studies of Novel Benzo‐ or 2,3‐Naphtho‐Fused Tetraazachlorins, Bacteriochlorins, and Isobacteriochlorins

“…[57] b,b,b',b'-Tetramethyltribenzotetraazachlorin (H 2 TBTAC, 1): Lithium (0.09 g, 13 mmol) was dissolved in hot dimethylaminoethanol (30 mL), to which a mixture of tetramethylsuccinonitrile (0.44 g, 3.2 mmol) and phthalonitrile (0.41 g, 3.2 mmol) was added at room temperature. The solution was slowly heated to reflux with stirring and then maintained at that temperature for 20 h, with occasional (every 5 h) addition of tetramethylsuccinonitrile (in total ca.…”