Etude par diffraction X des structures cristallines du furanne à la pression atmosphérique

Structure of 2,4,6-tris(N,N-dimethylamino)-1,3,5-oxadiazinium chloride dihydrate, C9H18N5O+.Cl−.2H2O

“…The heterocyclic nucleus exhibits partial double bonds and the' positive charge is not localized on the oxygen centre. Indeed, multiple bonding to O is relatively minor and the C-O distances of 1.366 (6) and 1.386 (5) A exceed by 0.02 A those in 4',6,7-trihydroxyflavylium chloride hydrate (IV) (Ueno & Saito, 1977) and are comparable with the 1.368 (6) A in furan (V) (Fourme, 1972 ',N, ,N,…”

Structure of N-(2-hydroxyethyl)-2-thiofuramide

“…Sikirica, Grdeni6 & Cimag (1982)consider the similar difference in di(2-furyl)mercury to be appropriate to the 2-furyl bond but not as a consequence of an Hg...O attraction. That steric reasons are not predominantly responsible for this feature is indicated particularly by its appearing in the crystal structure (a tetragonal form at 123 K) of unsubstituted furan (Fourme, 1972). Although the H atoms involved are determined with lower accuracy, the difference of 19 ° between the angles [115(2) and 134(2) ° ] is reliable enough and could be compared with the difference between H(5)-C(5)-O(1) and H(5)--C(5)-C(4) of 112(2) and 138 (2) ° respectively, in this compound.…”

Structure of N-(2-chloroethyl)-2-furamide

“…In the furan molecule itself (Fourme, 1972), the symmetrically identical C atoms bonded to the O atom are generally sp 2 hybridized, but there are considerable differences between the hybrid orbitals describing their three different bonds. The population of the p orbital of an atom between its hybrid orbitals is increased in the region of the bond to the more electronegative atom (Domenicano, Vaciago & Coulson, 1975, and references therein).…”

“…Fig. 1 is a (Fourme, 1972;Mata, Martin & Sorensen, 1978) as well as its derivatives. Different substituents at the C(2) and C(5) atoms do not change essentially the difference between the exocyclic angles (Gale~ir, Vlahov & Gale §ir, 1987, Table 3).…”

“…From the given angles, assuming that the hybrids on one centre are orthonormal (Maksir, 1986) and following the bond directions perfectly, the hybridization related to these bonds can be calculated. From the geometry of furan again (Fourme, 1972), the hybrid orbitals for the furan C(2)-C(3), C(2)-H(2) and C(2)-O(1) bonds were calculated to be sp LS, sp L2 and sp 4"4, respectively, where the numbers are the ratios of the p and s populations of the corresponding hybrids. As can be seen the s character of the C(2)-C(3)hybrid is slightly increased when compared with ideal sp 2 hybridization, the greatest s character is in the C(2)-H(2) hybrid orbital and as expected the hybrid toward the O atom has the greatest amount of p character.…”