Ammonia hydrogen bonding

Nelson, D. D., G. T. Fraser, and W. Klemper. 1987. Does ammonia hydrogen bond Science 238 1670-1674. 

Liquid ammonia is one of the best-known non-aqueous solvents and serves to illustrate some general points. For more detailed information various excellent review articles must be consulted -i solid ammonia hydrogen bonding has been established and similar considerations explain the considerable association in the liquid stated . 

Hydrogen bonds between —OH groups are stronger than those between —NH groups as a comparison of the boiling points of water (H2O 100 C) and ammonia (NH3 —33 C) demonstrates... 

Cellulose III. Cellulose III results from treatment of cellulose with Hquid ammonia (ammonia mercerization) or amines. Cellulose III can be made from either Cellulose I or II. When treated with water. Cellulose III can revert to its parent stmcture. Some cellulose III preparations are much more stable than other preparations. The intensities on diffraction patterns from Cellulose III differ slightly depending on whether the Cellulose III was made from Cellulose I or II, and thus these allomorphs are called IIIj or IHjj- Workers studying III concluded, based partiy on the results of I and II, that the packings of IIIj and IIIjj are parallel and antiparallel, respectively (67). IIIjj also is thought to have hydrogen bonds between the corner and center chains. 

Hydrogen bonding aeeounts for the abnormally high boiling points of, e.g., water, hydrogen fluoride, ammonia, and many organie eompounds (see later) sueh as aleohols. 

Amines, like ammonia NH3, are polar compounds and, except for tertiary amines, form intermolecular hydrogen bonds leading to higher boiling points than non-polar compounds of the same molecular weight, but lower boiling points than alcohols or acids. The smaller molecules, containing up to about six carbon atoms, dissolve in water. Aliphatic amines are similar in basicity to ammonia and form water-soluble salts with acids ... 

Factor b above is discussed in Sections II, B, 1 II, B, 4 and II, C. A hydrogen-bonded structure such as 221 can account for the facile reaction of 5-bromouracil or for the unique, so-called hydrolyzability of carboxymethylthio-azines (237). The latter may also react via the intramolecular mechanism indicated in 136. The hydrogen-bonded transition state 238 seems a reasonable explanation of the fact that 3,4,6- and 3,4,5-trichloropyridazines react with glacial acetic acid selectively to give 3-pyridazinones while other nucleophiles (alkoxides, hydrazine, ammonia, or sulfanilamide anion) react at the 4- and 5-positions. In this connection, 4-amino-3,5-dichloro-pyridazine in liquid hydrazine gives (95°, 3hr, 60%yield)the isomer-... 

The rate of reaction of a series of nucleophiles with a single substrate is related to the basicity when the nucleophilic atom is the same and the nucleophiles are closely related in chemical type. Thus, although the rates parallel the basicities of anilines (Tables VII and VIII) as a class and of pyridine bases (Tables VII and VIII) as a class, the less basic anilines are much more reactive. This difference in reactivity is based on a lower energy of activation as is the reactivity sequence piperidine > ammonia > aniline. Further relationships among the nucleophiles found in this work are morpholine vs. piperidine (Table III) methoxide vs. 4-nitrophenoxide (Table II) and alkoxides vs. piperidine (Tables II, III, and VIII). Hydrogen bonding in the transition state and acid catalysis increase the rates of reaction of anilines. Reaction rates of the pyridine bases are decreased by steric hindrance between their alpha hydrogens and the substituents or... 

These factors are sufficient to produce similar amounts of aminated isomers from 2,4-dichloropyrimidine which gives predominantly 4-alkoxylation products. Thus, a mixture of 2-amino-4-chloro- (302) and 4-amino-2-chloro-pyrimidine (303) is obtained on treatment of 2,4-dichloropyrimidine with alcoholic ammonia (25°, <18 hr), the reagent here being better at hydrogen bonding than piperidine. 

SOLUTION The N2 and C02 molecules are nonpolar (Chapter 7), so only dispersion forces are present. Both CHC13 and NH3 are polar molecules. Chloroform contains dipole forces as well as dispersion forces. Ammonia contains hydrogen bonds as well as dispersion forces. 

Ammonia is very soluble in water because the NH3 molecules can form hydrogen bonds to H20 molecules. Ammonia is a weak Bronsted base in water it is also a reasonably strong Lewis base, particularly toward d-block elements. For example, it reacts with Cu2+(aq) ions to give a deep-blue complex (Fig. 15.4) ... 

Amines are derived from ammonia by the replacement of hydrogen atoms with organic groups. Amides result from the condensation of amines with carboxylic acids. Amines and many amides take part in hydrogen bonding. 

Ammonia can form Hydrogen bonds with itself, whereas NF3 cannot. 

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