Physical Properties and Structures

It should be very important to reveal the structural features of heavy ketones and to make a systematic comparison with those of a carbonyl compound such as the bond shortening and the trigonal planar geometry which result from the sp2 hybridization between the carbon and oxygen atoms. 

Therefore, the elucidation of the intrinsic structural parameters of heavy ketones has to be done with kinetically stabilized systems. Most of the heavy ketones synthesized by steric protection with the Tbt group have provided single crystals suitable for X-ray structural analysis. The results for silanethione 38, germanethione 71b, germaneselones 75, 84, germanetellones 77,85, and stannaneselone 127, are summarized in Table III. 

It should be noted that all the M=X bond lengths observed here are significantly shorter than those reported for the corresponding double bond compounds stabilized by intramolecular coordination of heteroatoms. In other words, 

Although some examples of thermodynamically stabilized double bond systems between Group 14 and Group 16 elements showed trigonal planar geometry due to their structural restriction, almost all of their bond lengths are longer than those kinetically stabilized and theoretically predicted.67 These results clearly show that considerable electronic perturbation is inevitably involved in the thermodynamically stabilized systems. 

150 resonate at a much higher field -303 ppm (150a X=S) and -444 ppm (150b X=Se).68 This clearly shows that the thermodynamically stabilized tin-chalcogen double bonds in 150 (X=S, Se) are electronically perturbed to a great extent. 

In the last 25 years. X-ray diffraction analysis has been particularly widely used (along with other methods) to determine the structures of thienothiophenes. For example, the crystal structures of the following compounds were established by X-ray diffraction 3,4-dibromothieno[2,3-Z)]thiophene (86MI1), 2,2,5,5-tetramethyl- 

6- tetrahydrothieno[3,2-Z)]thiophene-2,6-dione (127) (the main chromophoric system of the thioindigo-like dye having the rranj -(5)-tranj-(5)-rra 5-configuration) (77CB1421, 78CB3233), (5-benzoyloxymethyl)thieno[2,3-Z)]thiophene-5-sulfamide 

Recently, it has been demonstrated that 2,5-bis(9-hydroxyfluoren-9-yl)thieno[2,3- 

The structures of l,3,4,6-tetraphenylthieno[3,4-Z)]thiophene (272) (83JA1705), 1,4-bis(rerr-butylthio)-3,6-diphenylthieno[3,4-c]thiophene, 4-(terr-butylthio)-3,6-diphe-nylthieno[3,4-c]thiophene-l(3//)-thione, 4-( rerr-butylthio)-3,6-diphenylthieno[3,4- 

Study of the crystal structure of sulfur-containing heterocyclic compound 292, prepared by the reaction of diethyl dihydroxythieno[2,3-Z)]thiophene-2,5-dicarbox-ylate with Lawesson s reagent in the presence of sulfur, revealed the presence of a three-dimensional S-S interaction (93ZN1621). 

The most remarkable feature of the molecular configuration of 1 is the narrow C-S-N angle of 92.2°10 (92.7°)9 in the five-membered ring, as a compromise between ring strain and angular distortion. The molecule as a whole (apart from the S-oxide oxygens) is practically planar. The crystal is built from centrosymmetric dimers, with N-H 0=C hydrogen bonds. 

The molecular structure of 7 reflects a compromise between maximum resonance, which would require an all-planar geometry and steric hindrance from the isopropyl substituents. The result is unusual. Not only has the benzene ring been squeezed by the pressure of bulky substituents R, and R2, but its plane has been forced to form an angle of 

Properties and Reactions of Bonds in Organic Molecules, p. 414. Longmans, Green, New York, 1968. 

6° 4 with the plane of the five-membered ring. Substituents Rj and R2 are coplanar with nitrogen, but their axis is turned out of the isothiazole plane by 14° 4. 12 Resonance states like 7a,12 which include the sulfoxide 

Since Rx and R2 in 7a are no longer equivalent with respect to their chemical environment as a result of restricted rotation, different sets of protons for Rx and R2 are observed in the NMR.14 

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Nakamura T, Tachibana H, Yumara M, Matsumoto M and Tagaki W 1993 Structure and physical properties of Langmuir-Blodgett films of Cgg with amphiphilic matrix molecules Synth. Met. 55 3131-6... 

GORDON, M., High Polymers—Structure and Physical Properties, Iliffe, London, 2nd Edn (1963) HILDEBRAND, J., and scoiT, R., The Solubility of Non-Electrolytes, Reinhold, New York, 3rd Edn (1949)... 

Hamada, T., Nishida, T., Sajiki, Y. and Matsumoto, M., Structures and physical properties of carbon fibers from coal tar mesophase pitch, J Mat Res, 1987, 2(6), 850 857. 

This chapter is devoted mostly to the discussion of the structure and physical properties of the enamines with a tertiary nitrogen atom, the emphasis being on enamines of cyclic ketones. 

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