Ammonia bond angle

In general, we know bond lengths to within an uncertainty of 0.00.5 A — 0.5 pm. Bond angles are reliably known only to one or twx) degrees, and there arc many instances of more serious angle enxirs. Tn addition to experimental uncertainties and inaccuracies due to the model (lack of coincidence between model and molecule), some models present special problems unique to their geometry. For example, some force fields calculate the ammonia molecule. Nlln to be planar when there is abundant ex p er i m en ta I evidence th at N H is a 11 i g o n a I pyramid. 

The H—O—H angle m water (105°) and the H—N—H angles m ammonia (107°) are slightly smaller than the tetrahedral angle These bond angle contractions are easily accommodated by VSEPR by reasoning that electron pairs m bonds take up less space than an unshared pair The electron pair m a covalent bond feels the attractive force of... 

The tetramethylammonium salt [Me4N][NSO] is obtained by cation exchange between M[NSO] (M = Rb, Cs) and tetramethylammonium chloride in liquid ammonia. An X-ray structural determination reveals approximately equal bond lengths of 1.43 and 1.44 A for the S-N and S-O bonds, respectively, and a bond angle characteristic bands in the IR spectrum at ca. 1270-1280, 985-1000 and 505-530 cm , corresponding to o(S-N), o(S-O) and (5(NSO), respectively. Ab initio molecular orbital calculations, including a correlation energy correction, indicate that the [NSO] anion is more stable than the isomer [SNO] by at least 9.1 kcal mol . ... 

In the CH4 molecule, the bond angle is the expected value, 109° 28. There are eight electrons around the carbon atom (four valence shell electrons from C and one from each H atom), which results in a regular tetrahedral structure. In the ammonia molecule, the nitrogen atom has eight electrons around it (five from the N atom and one from each H atom), but one pair of electrons is an unshared pair. 

FIGURE 23.3 (See color insert following page 302. ) Profiles of (a) energy and FF for nucleophilic attack and (b) electrophilic attack for distortion in the H-N-H bond angle of ammonia. 

TABLE 1. Calculated (MM2, MM3 and ab initio) and observed structural parameters for ammonia and methylamines (bond lengths in A, bond angles and tilt angles in degrees, dipole moments in Debye)5,6. Reprinted with permission from Refs. 5 and 6. Copyright (1985, 1990) American Chemical Society... 

The parent compound of all amines, ammonia, has a pyramidal structure with N—H bond lengths of 101.5 pm and H—N—H bond angles of 106.6°. The electronic structure of the ground state may be represented as... 

Ihe bond angles in ammonia are reduced to 107° by the action of a lone pair of electrons. 

The tetrahedral geometry resultant from these sp -hybridized nitrogen and oxygen atoms is found to exist in both ammonia and water. Bond angles in... 

Like ammonia, the structure is similar to the tetrahedral structure of methane. The two lone pairs repel each other in order to be as far apart as possible. The squeezing of the hydrogens in water is even greater than that in ammonia. The H-O-H bond angle in water is 104.5°. 

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