Bonded Carbon Compounds

Dartiguenave, Y. Dartiguenave, A. Gleizes, C. Saint-Joly, J. Galy, P. Meier, and A. E. Merbach, Inorg. Chem., 1978, 17, 3505. 

Calculations on [Fe(C5H5)(CO)2(CH2)] (30) (only isolated for substituted carbenes) show that there are suitable metal -orbitals perpendicularly disposed and although the orientation shown is favoured the calculated rotational barrier is only 6.2 kcal mol but this has not been determined experimentally. The car bene complexes [Fe(C5H5)(CO)L(RNHCNHMe)]+ (L=MeNC or tertiary phosphines) undergo intramolecular isomerization but this involves rotation about C—N rather than Fe—C bonds, and the rotational barriers (16.7—17.9 kcal mol ) are essentially independent of L and R.  

77 -Alkene and -alkyne Complexes.— There is well established evidence that an y -alkene can only change to co-ordination through the opposite ligand face by dissociation and recombination and not by any low-energy intramolecular rotation. Thus dissociation is required for racemization of /m/i5-l,2-disubstituted ethene, for example. However, rotation about the metal-alkene axis allows intramolecular changes, sometimes very rapid but sometimes too slow to lead to n.m.r. line-broadening. 

In [Mo(C5HB)Cl(PhC=CMe)2] the rotations of the alkynes are not independent. Compound (40) gives two cw-isomers, one of which is illustrated, and a trans-isomer which interconvert by aikyne rotation, but the rates of interchange of the trans- with the cis-isomers are not the same so that the rate of rotation of one aikyne is sensitive to the orientation of the other. 

---

DOUBLE-BONDED CARBON COMPOUNDS OR UNSATURATED CARBON BONDS... 

Double-bonded carbon compounds or unsaturated7 carbon bonds... 

The electrophilic character of mercuric salts towards 7r-bonded carbon compounds is well known Nucleophilic attack on the... 

When carbon forms a triple bond with another carbon, it is called an alkyne. Originally, triple-bonded carbon compounds were named after the simplest molecule, acetylene (C2H2), which is HC=CH. Dimethylacetylene is CH3C=CCH3. 

Of special interest are the multiply bonded carbon compounds, as typified by ethylene, acetylene, and COj. The geometry of these 3 molecules is the clue to the hybridization of the carbon atoms. Ethylene is a planar molecule in which the H—C—H and H—C—C bond angles are approximately 120° ... 

One of the cornerstones of the chemistry of carbon compounds (organic chemistry) is Kekule s concept, proposed in 1858, of the tetra-valence of carbon. It was independently proposed in the same year by Couper who, however, got little recognition (vide infra). Kekule realized that carbon can bind at the same time to not more than four other atoms or groups. It can, however, at the same time use one or more of its valences to form bonds to another carbon atom. In this way carbon can form chains or rings, as well as multiple-bonded compounds. 

Before we start with a systematic discussion of the syntheses of difunctional molecules, we have to point out a formal difficulty. A carbonmultiple bond is, of course, considered as one functional group. With these groups, however, it is not clear, which of the two carbon atoms has to be named as the functional one. A 1,3-diene, for example, could be considered as a 1,2-, 1,3-, or 1,4-difunctional compound. An a, -unsaturated ketone has a 1.2- as well as a 1,3-difunctional structure. We adhere to useful, although arbitrary conventions. Dienes and polyenes are separated out as a special case. a, -Unsaturated alcohols, ketones, etc. are considered as 1,3-difunctional. We call a carbon compound 1,2-difunctional only, if two neighbouring carbon atoms bear hetero atoms. 

Oxidation of olefins and dienes provides the classic means for syntheses of 1,2- and 1,4-difunctional carbon compounds. The related cleavage of cyclohexene rings to produce 1,6-dioxo compounds has already been discussed in section 1.14. Many regio- and stereoselective oxidations have been developed within the enormously productive field of steroid syntheses. Our examples for regio- and stereoselective C C double bond oxidations as well as the examples for C C double bond cleavages (see p. 87f.) are largely selected from this area. 

Unlike elimination and nucleophilic substitution reactions foimation of oigano lithium compounds does not require that the halogen be bonded to sp hybndized carbon Compounds such as vinyl halides and aiyl halides m which the halogen is bonded to sp hybndized carbon react m the same way as alkyl halides but at somewhat slowei rates... 

The product of addition of hydrogen cyanide to an aldehyde or a ketone contains both a hydroxyl group and a cyano group bonded to the same carbon Compounds of this type are called cyanohydrins... 

---