Secondary amines hydrogen bonding

Aviv and Gross developed an interesting insertion reaction of diazo compounds into a secondary amine-hydrogen bond in the presence of Fe-corrole complexes (Scheme 7.8) [12], Competition experiments performed in the presence of an amine and an alkene revealed the N—H-insertion reaction to be much faster than the cyclopropanation of the C=C bond. Apart from this chemoselectivity issue, the reactions are characterized by their very short reaction times most insertion reactions were completed within 1 min at room temperature. Most recently, Woo s group reported on a similar process using commercially available iron tetraphenyl-porphyrin [Fe(TPP)] dichloride [13]. 

One year later, Rahaman et al. reported a cascade reaction of aldehyde and nitro alkanes for the synthesis of functionalized y-nitro aldehydes with high reactivity [33], Generation of the intermediate nitro alkenes involved cooperative secondary amine/hydrogen bonding-promoted condensation of nitromethane and aldehydes. Consequently, the newly formed nitro alkenes promptly participated in the next cycle cocatalyzed by the two catalysts (Scheme 9.37). 

One method we have developed for avoiding polymerization with the adsorbed water layer is to use a base catalyzed reaction in supercritical CO2 (SCF CO2). We have shown that SCF CO2 has the unique property of removing all adsorbed water from the silica surface. Once removed the amine base catalyses the reaction of the silane with the surface. As shown in Figure 1, the preadsorbed amine hydrogen bonds to the surface silanol and renders the Si-0 group of the silanol more nucleophilic for reaction with the silicon atom of the incoming chloro or alkoxysilane. Triethylamine is the preferred amine as it binds to all isolated silanols from SCF CO2 and is not removed with subsequent exposure to flowing SCF CO2 solvent. Furthermore a tertiary amine should be used as primary and secondary amines such as ammonia are known to react with CO2 to produce carbamates. " ... 

The Concerted Bifunctional Mechanism. At the end of the 20th century, Noyori and co-workers reported a new hydrogen transfer mechanism in which a metal-hydride participates together with a primary or secondary amine NH bond (38,278,283,298). The hydrogen transfer catalytic activity of the isolated hydride intermediate allowed the authors to propose the outer-sphere mechanism outlined in Figure 93. The key intermediate is the six-membered metallacyle represented in the figure in which the metal-hydride and the NH functionality are interacting with the carbonyl bond. Theoretical studies support this mechanism and explain the encountered enantioselectivity (301,363-365). 

Primary and secondary amines can participate m mtermolecular hydrogen bonding but tertiary amines lack N—H bonds and so cannot... 

The presence of ammonia during hydrogenation suppresses formation of secondary amines and inhibits hydrogenation of double bonds in unsaturated nitriles. Eatty amines are used as corrosion inhibitors, flotation agents, quaternary salts for sanitizing agents and textile fabric softeners, and surface-active agents. 

Proline is the only amino acid in Table 27.1 that is a secondary amine, and its presence in a peptide chain introduces an amide nitrogen that has no hydrogen available for hydrogen bonding. This disrupts the network of hydrogen bonds and divides the peptide into two separate regions of a helix. The presence of proline is often associated with a bend in the peptide chain. 

Apparently, cyclization involves the formation of open-chain intermediates 342, 343, further closing up to imidazolidines 344 and oxazolidines 345 which eliminate the secondary amine, thus leading to imidazolines 346 and oxazolines 347. The latter exist in the solution exclusively in the enolic forms 348, 349 which are stabilized by conjugation and intramolecular hydrogen bonds. 

Like alcohols, amines with fewer than five carbon atoms are generally water-soluble. Also like alcohols, primary and secondary amines form hydrogen bonds and are highly associated. As a result, amines have higher boiling points than alkanes of similar molecular weight. Diethylamine (MW = 73 amu) boils at 56.3 °C, for instance, while pentane (MW = 72 amu) boils at 36.1 °C. 

With secondary amines, cleavage of the bond j8 to the nitrogen atom occurs preferentially at the shortest hydrocarbon chain. If the shortest hydrocarbon chain has three or more carbon atoms, a, /3-cleavage occurs with a hydrogen rearrangement. 

Hydrogen bonding 5, occurs when a proton-acceptor molecule (primary and secondary amines, and sulfoxides) interacts with a proton-donor molecule (alcohols, carboxylic acids, and phenols). 

A protein s secondary structure arises from the formation of intra- and inter-molecular hydrogen bonds. All carboxyl group oxygens and amine hydrogens of a polypeptide participate in H-bonding. Protein secondary structure also derives from the fact that although all C-N bonds in peptides have some double bond character and cannot rotate, rotation about the Co-N and Ca-C bonds is possible and is... 

---