Hydrogen on Carbon

We give few references in this section and the various specialist reviews should be consulted by the interested reader, which include an extensive review of the data for metal carbonyl complexes.  

---

Ketones oxidize about as readily as the parent hydrocarbons or even a bit faster (32). Although the reactivities of hydrogens on carbons adjacent to carbonyl groups are perhaps doubled, the effect is small because one methylene group is missing in comparison to the parent hydrocarbon. Ketones oxidize less readily than similar primary or secondary alcohols (35). 

Those epimers of 1,2,3,4-tetrahydro-j8-carbolines of general structure 139, in which the hydrogen on carbon-1 of the carboline moiety is axial, are converted into the corresponding 3,4-dihydro- -carbolinium salts (141) by mercuric acetate oxidation. Sodium dichromate... 

The effects of hydrogen on carbon and low-alloy steel equipment ... 

Hydrogens on carbon next to aromatic rings also show distinctive absorptions in the NMR spectrum. Benzylic protons normally absorb downfield from other alkane protons in the region from 2.3 to 3.0 5. 

Hydrogens on carbon next to an ether oxygen are shifted downfield from the normal alkane resonance and show U-f NMR absorptions in the region 3.4 to 4.5 8. This downfield shift is clearly seen in the spectrum of dipropyl ether shown in Figure 18.4. 

Hydrogens on carbon next to a carbonyl group are acidic. In general, a /3-dicarbonyl compound is most acidic, a ketone or aldehyde is next most acidic, and a carboxylic acid derivative is least acidic. Remember that alcohols, phenols, and carboxylic acids are also acidic because of their -OH hydrogens. 

Table 3. Electrocatalytic hydrogenations on carbon felt electrodes coated with polyviologen/Pd...

The intermediate Jt-allyl complex is formally the palladium(II) complex of an allylic anion that can be represented by the two mesomeric forms shown in Scheme 17.2. It is important to note that this is not a fast equilibrium between two cr-allyl complexes but a stable species where palladium is simultaneously bound to both carbon-1 and carbon-3. All eight atoms of the Jt-allyl moiety are almost in the same plane. All three carbon atoms have sp2 character and the rotation between the Cl-C2 and C2-C3 bonds is blocked. As a consequence of the hindered rotation, four dia-stereomeric Jt-allyl complexes are possible. For example, in Scheme 17.2 both R and R are syn to the hydrogen on carbon-2, therefore this complex is called the syn,syn diastereomer. 

TABLE 22.2. Contributions of Primary CH3 Substitution Groups Replacing Hydrogen on Carbon... 

Figure 4. X-ray crystal structure of compound 12 (toxin C4), determined by S. D. Darling at the University of Akron. The calculated positions of hydrogens on carbons 5, 6, and 11 have been shown for clarity.

They consist of two sugars that are identical except that the deoxyribose contains a hydrogen on carbon 2 (thus the name deoxy or without one oxy or hydroxyl Figure 10.7). These specific compounds were originally obtained from yeast (DNA) and the thymus gland (RNA). 

Just as by the reducing action of hydrogen on carbon dioxide formic acid, formaldehyde, methyl alcohol and methane may be directly or... 

Sherman and Eyring (14) from theoretical considerations proposed that in case of the chemisorption of hydrogen on carbon the activation energy... 

Figure 20 Complex 52 [Mnm(Ll 1)]2. The hydrogens on carbon atoms have been omitted for the sake of clarity.

As an example, Fig. 6 shows the experimental isotherms of the adsorption and desorption of hydrogen on carbon fiber Busofit-M8 and wood-based activated carbon WAC 3-00 at the nitrogen temperature. Absence of an appreciable hysteresis confirms that reversible physisorption exclusively takes place with all investigated materials. 

---