Ethanes tetrahedra

K. G. R. Pachler, Extended Hiickel theory MO calculations of proton-proton coupling constants-II. The effect of substituents on vicinal couplings in monosubstituted ethanes, Tetrahedron, 27 (1971) 187-199. 

D Anna, R, Frenna, V, Pace, V and Noto, R., Effect of ionic liquid organizing ability and amine structure on the rate and mechanism of base induced elimination of l,l,l-tribromo-2, 2-bis(phenyl-substituted)ethanes. Tetrahedron 62,1690-1698 (2006). 

If this carbon holds in different atoms, the bond angles are somewhat (a little) changed and the tetrahedron ceases to be regular. But the real foundation for conformational study was laid in 1935 when it was observed that there was discrepancy between the entropy of ethane as found from the heat capacity measurements and as calculated from spectral data. From this the physical chemists concluded that there must be hindrance to rotation about the carbon bond in ethane. Later it was found that there was tortional barrier to free rotation to the extent of about 2.8 K cals per mole. 

Carbon atoms bonded to four other atoms are each at the center of a tetrahedron. As shown below for ethane, H3C-CH3, the two tetrahedrons are joined so that the central carbon atom of one is a corner atom of the other. 

Acces aux (R)S acyl-1 vinyl p-tolylsulfoxydes a partir du (R)S dimefhylamino-2p-tolylsulfinyl-1 ethane. Leurs reactivites en tant que dieno-phile. Tetrahedron Lett. 1986, 27, 2693—2606. 

Figure 7. Modeling the C-C rotation in ethane, (a) Only the right hand tetrahedron moves (b) the cycle starts with the eclipsed Dih rotamer (c) one of the six chiramers (see text) (d) the Did staggered rotamer.

Fujimura, M., Nakazawa, T and Murata, I., A novel coupling reaction of 1-azulylmethyl-trimcthylammonium iodide synthesis of l,2-bi.s(I-azulyl)ethane and 12.2.2.21(1.3)-azulenophane. Tetrahedron Lett., 825, 1979. 

Hydrazine is similar to ethane, but with a lone pair replacing a hydrogen atom on each of the central atoms. There is free rotation around the nitrogen/ nitrogen single bond. In the protonated form, the geometry around each nitrogen atom is still based on the tetrahedron. 

Monti, D., Gramatica, P., Speranza, G., and Manitto, P, A convenient synthesis of both the anomers of ethyl (2,3,4,6-tetra-O-benzyl-D-glucopyranosyl)acetate, Tetrahedron Lett., 28, 5047, 1987. Scremin, C.L., Boal, J.H., Wilk, A., Phillips, L.R., Zhou, L., and Beaucage, S.L., l-(2-Deoxy-a- and P-D-e yf/ rc>-pentofuranosyl)-2-(thyniin-l-yl)ethane derivatives as conformational probes for (z/fDNA ohgonucleotides. Tetrahedron Lett., 36, 8953, 1995. 

Yamano, T., Taya, N., Kawada, M., Huang, T., and Imamoto, T., Enantioselective hydrogenation of P-keto esters catalyzed by P-chiral i>zT(dialkylphosphino)ethanes-Ru(n), Tetrahedron Lett., 40, 2577, 1999. 

Figure 2.1. (A) The tetrahedral model for methane. The small black spheres represent the positions of the hydrogen atoms surrounding the tetrahedron of carbon. (B) Ethane, C2H6, with a pair of singly bonded carbon atoms. (C) Ethylene, C2H4, with a pair of doubly bonded carbon atoms. (D) Acetylene, C2H2, with a pair of triply bonded carbon atoms.

Fig. 10.40. Relationship between TS structure and stereoselectivity in [2,3]-sigmatropic rearrangement of alloxy carbanions (a) early TS for unsubstituted allyloxymethyl anion (b) tighter cyclic TS for stabilized allyloxypropargyl anion (c,d) preferred conformation of E-and Z-crotyloxypropargyl anions leading to the E anti and Z syn stereoselectivity (e,f) unchelated and chelated TSs for a-crotyloxy ethanal enolate leading to the E syn stereoselectivity. Reproduced from Tetrahedron, 50, 5917 (1994), by permission of Elsevier.

Oohara N, Katagiri K, Imamoto T (2003) A novel P-chirogenicphosphine ligand, (S, S)-l,2-bis-[(ferrocenyl)methylphosphino]ethane synthesis and use in ihodium-catalyzed asymmetric hydrogenation and palladium-catalyzed asymmetric allylic alkylation. Tetrahedron Asymmetry 14 2171-2175... 

Miyazaki T, Sugawara M, Danjo H, Imamoto T (2004) Dihydroboronium derivatives of (S, S)-l,2-bis(t-butylmethylphosphino)ethane as convenient chiral ligand precursors. Tetrahedron Lett 45 9341-9344... 

It is possible to extend the VSEPR rules to repulsions between bond pairs on adjacent atoms. The extension is straightforward the best structures would be the ones that place these bonds as far apart as possible. As an example, consider the already familiar molecule ethane, H3C—CH3. Since each carbon is surrounded by four electron pairs, it will assume a geometry derived from a tetrahedron, with angles of 109°, as shown in Scheme 7.8a. 

A soln. of l-/ r/-butyldimethylsilyl-2-chloro-l-ethanone in THF added dropwise during 15 min to a stirred soln. of Li-2,2,6,6-tetramethylpiperidide in the same solvent at —78° under argon, after 30 min methyl vinyl ketone added, the mixture allowed to warm to room temp, during 1 h, and half-satd. NH4CI soln. added after a further 30 min-> l-[2-(/er/-butyldimethylsilyloxomethyl)cyclopropyl]ethan-l-one. Y 75-89% cis Jrans 1.9 1). F.e., also from a-sulfonioacylsilanes, s. J.S. Nowick, R.L. Danheiser, Tetrahedron 44, 4113-34 (1988). 

Isopropylmagnesium bromide in ether added dropwise to a stirred, ethereal suspension of (Z)-1,4-di(2-tetrahydropyranyloxy)-but-2-ene and a little dichloro[l,2-bis(di-phenylphosphino)ethane]nickel(II) at 0°, the mixture left aside at room temp, for 48 h, and hydrolyzed with satd. NH4CI soln. - product. Y 95%. F.e. and limitations s. R. Menicagli et al.. Tetrahedron Letters 29, 3373-4 (1988). 

The principles used to describe the bonding for methane can be extended to larger molecules that have additional carbon atoms and carbon-carbon bonds rather than only the C-H bonds found in methane. Ethane (5) has a covalent bond between two carbon atoms, for example, and both carbons have four bonds directed to the corners of a tetrahedron. The structure of ethane is shown in Figure 3.12, first with the Lewis dot formula for ethane (5a) and then as a structure made by overlapping two tetrahedrons of carbon (5b), each carbon with three hydrogen atoms and the fourth bond between carbon and carbon. The carbon-carbon bond is represented by overlap of the tetrahedrons in 5b. 

Demir, A. S. Sesenoglu, O. Aksoy-Cam, H. Kaya, H. Aydogan, K. Enantioselective Synthesis of Both Enantiomers of 2-Amino-2-(2-Furyl) Ethan-l-ol as a Flexible Building Block for the Preparation of Serine and Azasugars. Tetrahedron Asymmetry 2003,14,1335-1340. 

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