Melting point multiple

The spectral properties of benzobarrelene are as follows infrared (potassium iodide) cm. strong peaks 1460, 1325, 790, 750, 690, 660 proton magnetic resonance (chloroform-d) S (multiplicity, number of protons, assignment) 4.9 (multiple , 2, bridgehead H), 6.8-7.3 (multiple , 8, aryl and vinyl H). The reported melting point is 65.5-66°.From 20 g. of tetrachlorobenzo-barrelene the submitters obtained 8.3-8.8 g. (79-83%) of benzobarrelene, m.p. 64-65°. 

The checkers dried the product in a vacuum desiccator for 24 hours to remove all the 2-propanol and obtained 77-79 g. (64-66%), m.p. 70-72°. The yield reported by the submitters was 82-89 g. (68-74%), m.p. 73—74°. The literature melting point is 66-67°. The product has the following spectral properties 90-MHz. proton magnetic resonance (chloroform-d) d (multiplicity, number of protons, assignment, coupling constant J in Hz.) 2.84... 

The proton magnetic resonance spectrum of the product in chloroform-d has the following absorptions S (multiplicity, number of protons, assignment) 5.45 (multiplet, 2, bridgeheadH), 6.95 (multiplet, 4, vinyl ff). A melting point of 125° is reported in the literature. ... 

Magnetic quantum number. 19 Magnetic susceptibility mass. 460-463 molar, 461 volume, 460 Maim. J. O.. 70 Map of twist angles, 490 Marcus theory, 571 Mass spectrometry. 239 Maximum multiplicity, 26-27 Mechanisms inner sphere, 565-567 outer sphere. 558-561 of redox reactions. 557-572 of substitution reactions. 545-547. 551-553 Medicinal chemistry, 954-960 Meissner effect, 285 Melting points, and chemical forces. 307-310... 

Multiple melting points due to different solid-phase modifications... 

Multiple Melting Points A compound may have different crystal structures (i.e., solid phases). For example, carbon tetrachloride has three known solid phases at atmospheric pressure la (face-centered cubic), lb (rhombohedral), and II (monoclinic). Ia and lb melt at temperatures some 5K apart [3]. Multiple melting points have been reported for a large set of compounds, such as many of those listed in the Merck Index [4], Dearden and Rahman improved a structure-melting point correlation for substituted anilines by excluding two outliers on the ground that their Tm values were inadequate, due to different crystalline forms [5]. 

In many instances, TGs exist in polymorphic forms. Crystal structure is very important to the properties of margarines, shortenings, and specialty fats. The very unstable a form is readily transformed to the more stable ft form, which in some TGs has a higher melting point (more stable) than the /3 form. In single-acid TGs, the order is a — f3 — a, but some mixed TGs show a lower-melting (less stable) (3 form. This is further complicated by the existence of multiple / and /3 forms, depending upon the detailed TG structures at hand. 

CH" 7t bonds work cooperatively. The weak directionality of CH-tt interactions and the large surfaces offered by n systems means that many aromatic compounds exhibit multiple such interactions. While they are individually weak their combined, cooperative effect can be very significant. The existence of CH-n interactions is manifest in the commonly higher melting points and facile crystallisation of aromatic compounds compared to aliphatic compounds of similar molecular weight. 

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