17O NMR spectroscopic study of steric hindrance in phthalic anhydrides and phthalides

17O nuclear magnetic resonance spectroscopic study of substituted phthalic anhydrides and phthalides

“…Molecular mechanics calculations (MM2) were carried out on this series (If-li). In-plane distortions were found to be similar to that calculated for l c (22). Apparently the increase in halogen size is offset by the lengthening halogen-carbon bond distance, resulting in the effective steric interactions remaining roughly constant.…”

“…The two substituents that lead to large downfield shifts, 3-tert-butyl I d (22 ppm) and 3-nitro 1 j (21 ppm), exhibit opposite electronic effects, the former a moderate electron donor, the latter strongly electron withdrawing. In the case of I d the large effective size causes larger in-plane distortions and presumably gives rise to increased repulsive van der Waals interactions (22). The large downfield shift for l j is a composite of.…”

“…The utility of 170 nrnr spectroscopy has been rapidly increasing (10)(11)(12), and it has been successfully used to estimate electronic characteristics (13)(14)(15) and local environment changes arising from steric interactions for a number of functional groups (16)(17)(18)(19)(20)(21), including carbonyl groups (1 8-21). For example, it has been recently demonstrated that large bulky groups (e.g., tert-butyl) cause considerable in-plane distortion of the molecular structure of phthalic anhydride when placed at the 3 position (22). The steric interactions were reflected in the 170 chemical shift data of these compounds.…”

Diacyltelluride: Synthesen durch Reaktionen von Acylchloriden mit Bis(trialkylsilyl)telluriden; Strukturbestimmungen an Di(1-adamantoyl)tellurid und Adamantancarbonsäureanhydrid

“…Am Beispiel der Neopentyl-, Isopropyl-und tButyl-Verbindungen 5, 3 und 8 lassen sich die Effekte von α-und b-Verzweigung erkennen: der gegenla È ufige Gang der relativen 13 C-und 125 Te-Verschiebungsa Èn-derungen korreliert gut mit fru È heren 13 C-und 17 O-NMR-Befunden an Carbonsa È uremethylestern [12]. Verglichen mit 3±9, in denen RC(=O)TeR'-Gruppierungen vorliegen, erscheinen in Telluroestern mit C=Te-Doppelbindungen 13 C-und 125 Te-Signale bei noch wesentlich tieferen Feldern [3,4,13].…”

Synthesis, 17O NMR spectroscopy and structure of 2-trifluoroacetyl-1-methoxycycloalkenes

“…On the other hand, since the 60s, 17 O NMR spectroscopy is becoming an increasing important method in organic chemistry for examining a wide variety of structural problems [8] and it provides insights into the understanding of chemical reactivity [9].…”