Primary hydrogens

A single secondary hydrogen m butane is abstracted by a chlorine atom 3 9 times faster than a single primary hydrogen... 

Assuming the relative rate of secondary to primary hydrogen... 

A similar study of the chlorination of 2 methylpropane established that a tertiary hydrogen is removed 5 2 times faster than each primary hydrogen... 

Breaking a bond to a primary hydrogen atom m propene requires less energy by 42 kJ/mol (10 kcal/mol) than m propane The free radical produced from propene is allylic and stabilized by electron delocalization the one from propane is not... 

Between 6 and 30% of the radical attack on butane may occur at the primary hydrogen atoms (213). Since ca 6% of the butane goes to or through butyric acid (22), the middle of this range does not seem unreasonable. Because it is much more resistant to oxidation than its precursors or coproducts, acetic acid (qv) is the main product of butane LPO. 

The value of k /k can be determined by measuring the ratio of the products 1-chlorobutane 2-chlorobutane during the course of the reaction. A statistical correction must be made to take account of the fact that the primary hydrogens outnumber the secondaiy ones by 3 2. This calculation provides the relative reactivity of chlorine atoms toward the primary and secondary hydrogens in butane ... 

Similar preference in replacement by fluorine of tertiary versus secondary and secondary versus primary hydrogens is observed in the fluorination of alkanes with chlorine trifluoride in 1,2-difluorotetrachloroethane at room temperature (Table 3). Skeletal rearrangements accompany the fluorination [31]... 

Photochemical chlorination of pentane gave a mixture of three isomeric monochlorides. The principal monochloride constituted 46% of the total, and the remaining 54% was approximately a 1 1 mixture of the other two isomers. Write structural formulas for the three monochloride isomers and specify which one was formed in greatest amount. (Recall that a secondary hydrogen is abstracted three times faster by a chlorine atom than a primary hydrogen.)... 

From these and similar reactions, it s possible to calculate a reactivity order toward chlorination for different sorts of hydrogen atoms in a molecule. Take the butane chlorination, for instance. Butane has six equivalent primary hydrogens (-CH3) and four equivalent secondary hydrogens (-CH2-). The fact that butane yields 30% of 1-chlorobutane product means that each one of the six primary hydrogens is responsible for 30% -e 6 = 5% of the product. Similarly, the fact that 70% of 2-chlorobutane is formed means that each of the four secondary hydrogens is responsible for 70% -e 4 = 17.5% of the product. Thus, reaction of a secondary hydrogen happens 17.5% + 5% = 3.5 times as often as reaction of a primary hydrogen. 

A similar calculation for the chlorination of 2-methylpropane indicates that each of the nine primary hydrogens accounts for 65% + 9 = 7.2% of the product, while the single tertiary hydrogen (R3CH) accounts for 35% of the product. 

Preeclampsia, Viagra and, 164 Prelog, Vladimir, 181 Prepolymer, epoxy resins and, 673 Priestley, Joseph, 245 Primary alcohol, 600 Primary amine, 916 Primary carbon. 84 Primary hydrogen, 85 Primary structure (protein), 1038 Primer strand (DNA), 1108 pro-R prochiralitv center, 316 pro-S prochirality center, 316 Problems, how to work, 27 Procaine, structure of, 32 Prochirality, 315-317 assignment of, 315-316 naturally occurring molecules and, 316-317... 

It has been proposed that aromatic solvents, carbon disulfide, and sulfur dioxide form a complex with atomic chlorine and that this substantially modifies both its overall reactivity and the specificity of its reactions.126 For example, in reactions of Cl with aliphatic hydrocarbons, there is a dramatic increase in Ihe specificity for abstraction of tertiary or secondary over primary hydrogens in benzene as opposed to aliphatic solvents. At the same time, the overall rate constant for abstraction is reduced by up to two orders of magnitude in the aromatic solvent.1"6 The exact nature of the complex responsible for this effect, whether a ji-coinplex (24) or a chlorocyclohexadienyl radical (25), is not yet resolved.126- 22... 

In proceeding to a consideration of the chemical ionization mass spectra of more highly branched paraffins, it will be most convenient to consider separately the several different classes of alkyl ions found in the spectra—i.e., MW — 1+, MW — 15+, MW — 29 +, etc. We can see from Table II that a considerable amount of variation in the relative intensity of the MW — 1 ions (always the highest mass ion for which an intensity is given in the table) occurs. However, we shall show that the observed MW — 1 intensities can be approximately accounted for in terms of the concept of localized electrophilic attack by the reactant ion. First, however, we must consider the energetics of two processes which may be important in generating the spectra of branched paraffins. One of these is the abstraction of a primary hydrogen by the reactant ion. As a typical example we may write... 

Experiments were made with pure 2-propanol samples stored for six months in white glass containers, which were half full and exposed to the light. It could be proved that peroxides form in these conditions. The experiment showed that peroxidation is faster when a ketone is present. The fact that this oxidation only takes place with secondary alcohols shows that it affects the hydrogen atom in the a position of the active group, (atom that is more reactive than a primary hydrogen), and not the actual function. 

B- HCCH involving weak primary hydrogen bonds Z- HCCH have revealed large non-linearities, but with an angle 0 that remains reasonably close to those predicted by the rules. Figure 22 illustrates this result through the experimentally determined geometries for the cases when B is 2,5-dihydrofuran [200], oxirane [201], formaldehyde [202], thiirane [203], and vinyl fluoride [204], On the other hand, as noted in Sect. 3.1.3, both... 

The reaction network for 5,6-benzoquinoline [101] has been proposed in a more detailed level than that of acridine. In this network, conversely to acridine network, only one primary hydrogenation product, l,2,3,4-tetrahydro-5,6-benzoquinoline, was identified, and in contrast to the quinoline case however, no aniline derivatives were detected. 

In the condensation of alkyl methyl ketones with esters, the primary hydrogen is the one lost as in the reactions previously discussed with carbon dioxide, aldehydes, etc. The reaction is with the more rapidly formed and less hindered ion rather than with the ion that would be present in higher concentration at equilibrium. 

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