Electron pair non-bonding

Halonium ions, including hydrido or alkylhalonium ions, are similarly protolytically activated, indicative of protonation of the non-bonded electron pairs of their halogen atoms. 

Lewis acid catalysts, such as AlCl or BF, coordinate strongly with non-bonded electron pairs but they iateract only weakly with bonded electron pairs. Therefore, n-donon reagents, such as alkyl haUdes, can react with Lewis acid catalysts even under complete exclusion of moisture or any other proton source ... 

Earlandite structure, 6,849 Edge-coalesced icosahedra eleven-coordinate compounds, 1, 99 repulsion energy coefficients, 1,33,34 Edta — see Acetic acid, ethylenediaminetetra-Effective atomic number concept, 1,16 Effective bond length ratios non-bonding electron pairs, 1,37 Effective d-orbital set, 1,222 Egta — see Acetic acid,... 

Efg Electric field gradient n-pair Non-bonding electron pair Tt-pair -bonding electron pair XY Generalised dihalogen molecules... 

Fig. 1 Comparison of the experimentally determined geometries of the hydrogen-bonded complex H3N-- -HC1 and its halogen-bonded analogue H3N- C1F (both drawn to scale) with a non-bonding electron-pair (n-pair) model of NH3. Here, and in other figures, the n-pair electron distribution is drawn in the exaggerated style favoured by chemists. The key to the colour coding of atoms used in this and similar figures is also displayed...

Furan is the prototype of molecules that carry both non-bonding and aromatic tt bonding electron pairs. The usual model for the n-pair and tt electron density in this molecule is shown in Fig. 18. The oxygen atom is taken to have a non-bonding electron pair in an orbital whose symmetry axis coincides with the C2 axis of furan. 

The non-bonding electron pair may occupy one orbital with antiparallel spins (singlet, V2), or two different orbitals with antiparallel (singlet, lcrp) or parallel spins (triplet, 3crp). 

The non-bonding electron pair occupies an s-orbital, the bonding electrons occupy p-orbitals, while the third p-orbital remains empty. The bonding angle should be strictly 90° (geometry A). 

For the coordination number 3, two different environments of tin(II) can be distinguished. One is the trigonal planar arrangement which is realized when the non-bonding electron pair at the tin atom is engaged in bonding, with tin acting as a Lewis base. The first example of this kind characterized by X-ray structural analysis is compound 4 30) (for the structure see also Chapter 5). 

Stannylenes are in the first place Lewis acids (electron acceptors) as can be easily derived from the structures of the solids (Chapter 3). When no Lewis bases (electron donors) are present, they may also act as Lewis bases via their non-bonding electron pair (see polymerization of organic stannylenes). 

In contrast to carbenes the singlet electron configuration in stannylenes SnX2 is much more stable this implies that the non-bonding electron pair can remain unchanged during a reaction. Consequently, this reaction center and other centers must be considered in a reaction pathway multiplying the reaction possibilities compared with the isoelectronic carbenes. 

The rationalization of the conformational anomeric effect solely based on electrostatic interactions fails to account for these solvent effects. Another interpretation based on bond polarizability in 1,1-dialkoxyalkyl systems calls electronic transfer from a non bonding electron pair of one oxygen atom to the empty cr c 0 orbital from the other alkoxy substituent (Fig. 10).16... 

A Central atom, X Atoms bonded to central atom, E Non-bonding electron pairs... 

HOMO-LUMO) interactions the LUMO being the antibonding cr x orbital [45], the HOMO a non-bonded electron pair, formally available at both 90° and about 180° to the C-X bond [46], Much similar work supports this interpretation. Contacts between halogens (X) and electrophilic centres E (all metal ions) [47] fall almost exclusively in the range 9O<0E<12O°, while, for better electron donors Nu, 0Nu generally lies between 150° and 180°. 

The ready formation of the episulphonium compound is reasonably explained in terms of the directionality and polarizability of the non-bonded electron-pairs of sulphur, a soft nucleophile which naturally forms bonds at angles close to 90°. We may presume that the directional requirements of the nucleophilic orbitals of first-row elements (N, O) are stricter, and that this factor shows up most clearly in a situation (the formation of a three-membered ring) which makes extreme demands on orbital flexibility. 

Compare the flexibility of the geometry of hydrogen-bonding to the non-bonding electron-pairs of neutral oxygen elicited by the demands of crystal forces (Donohue, 1968)... 

The inner shell d orbitals are assumed not to be involved in the bonding but instead comprise non-bonding electron pairs. 

Calculate the number of bonding and non-bonding electron pairs around the central atom in each of the following species and work out the shape of the molecule or ion ... 

The closo-tetraphosphorus sulfides, with their various stoichiometries and unique structures (Scheme 2), exhibit multiple and often distinct potential coordination sites. These sites often involve several distinct sets of formally non-bonding electron pairs at both phosphorus and sulfur atoms, and the tetraphosphorus sulfides could therefore be expected to exhibit a wide range of coordination modes and original behavior towards Lewis acids. But so far this has not proved so. 

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