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Donation of bonding electrons

When carbon forms four covalent bonds with halogen atoms the second quantum level on the carbon is completely filled with electrons. Most of the reactions of the Group IV tetrahalides require initial donation by a Lewis base (p. 91) (e.g. water, ammonia) which attaches initially to the tetrahalide by donation of its electron pair. Hence, although the calculated free energy of a reaction may indicate that the reaction is energetically favourable, the reaction may still not proceed. Thus we find that the tetrahalides of carbon... [Pg.195]

An ionic bond is formed by the donation of an electron by one atom to another so that in each there is a stable number of electrons in the outermost shell (eight in the case of most atoms). An example is the reaction of sodium and chlorine Figure 5.1). [Pg.77]

There is clearly a conceptual relationship between the properties called nucleophilicity and basicity. Both describe a process involving formation of a new bond to an electrophile by donation of an electron pair. The pA values in Table 5.7 refer to basicity toward a proton. There are many reactions in which a given chemical species might act either as a nucleophile or as a base. It is therefore of great interest to be able to predict viiether a chemical species Y P will act as a nucleophile or as a base under a given set of circumstances. Scheme 5.4 lists some examples. [Pg.292]

First, look at the reaction and identify the bonding changes that have occurred. In this case, a C—Br bond has broken and a C-C bond has formed. The formation of the C-C bond involves donation of an electron pair from the nucleophilic carbon atom of the reactant on the left to the electrophilic carbon atom ol CH Br, so we draw a curved arrow originating from the lone pair on the negatively charged C atom and pointing to the C atom of CH3Br. At the same time the C—C bond forms, the C-Br bond must break so that the octet rule is not violated. We therefore draw a second curved arrow from the C-Br bond to Br. The bromine is now a stable Br- ion. [Pg.151]

When the structures for many ligands (e.g., H20, NH3, C032-, and C2042-) are drawn, there is no question as to which atom is the electron pair donor. Ligands such as CO and CN normally bond to metals by donation of an electron pair from the carbon atom. It is easy to see why this is so when the structures are drawn for these species and the formal charges are shown. [Pg.582]

In compounds (4) and (5), whose structures are shown in Fig. 3, there are also electrons available for M-NO or M-CO tt bonding after all other bonds have been provided for. In (4) there are four such electrons and in (5) there are six. It may also be that the bridging CO or NO groups require relatively little (or even no) back-donation of metal electrons (although this is an unsettled question), but even if they do, in (4) and (5) there is one electron pair per bridging ligand, which would be quite sufficient even for a terminal CO or NO ligand. [Pg.207]

The picture sketched above disagrees with the frequently used donation/back donation model of adsorbed CO. This model describes the chemisorption bond in terms of donation of electrons from the CO 5a orbital into empty orbitals at the surface of the metal, and back donation of d-electrons from the metal to the unoccupied 2n level of CO. The back donation is essentially correct, but the donation is not. [Pg.315]

Moreover, the phthalonitrile process has the added advantage of being the more elegant of the two syntheses. This technique makes it possible to produce comparatively pure copper phthalocyanine without obtaining substantial amounts of side products, a phenomenon which is understandable in view of the fact that the phthalonitrile molecule provides the parent structure of the phthalocyanine ring. Formally, rearrangement of the bonds necessitates donation of two electrons to the system ... [Pg.427]

HC1 is the acid, because it is donating an H+ and the H+ will accept an electron pair from ammonia. Ammonia is the base, accepting the H+ and furnishing an electron pair that the H+ will bond with via coordinate covalent bonding. Coordinate covalent bonds are covalent bonds in which one of the atoms furnishes both of the electrons for the bond. After the bond is formed, it is identical to a covalent bond formed by donation of one electron by both of the bonding atoms. [Pg.76]

Ion pairing is due to electrostatic forces between ions of opposite charges in a medium of moderate to low relative permittivities. It should be distinguished from complex formation between metal cations and anionic ligands, in which coordinative bonds (donation of an electron pair) takes place. One distingnishing feature is that, contrary to complex formation, the association is nondirectional in space. The association of a cation and an anion to form an ion pair can, however, be represented as an equilibrium reaction by analogy to complex formation with an equilibrium constant A)ass [3,5]. If a is the fraction of the electrolyte that is dissociating into ions and therefore (1 - a) is the fraction that is associated, then... [Pg.69]

This orbital is antibonding between carbon and iodine, meaning that donation of the electron pair from cyanide will cause the Cl bond to weaken and eventually break. [Pg.65]

The carbyne ligand may be viewed as a three-electron donor, similar to the nitrosyl ligand, with a pair of electrons in an sp orbital and a single electron in a p orbital. Donation of the sp electrons and pairing the p electron with one from the metal atom gives a a bond and a 7r bond, respectively. The second rbond results from donation of an electron pair from the metal atom to the empty p orbital of the ligand. [Pg.342]

Class IB ions adsorb to a much greater extent than do class 1A ions because the attraction between adsorbate and electrode extends beyond simple coulombic forces to covalent bonding with the electrode via donation of adsorbate electrons to orbitals on the electrode surface. Examples of class IB ions, in order of increasing strength of interaction with the electrode, are the anions CP < Br < I- S042- S202- NCO NCS . [Pg.44]

The arrow in 11a symbolizes donation of tt electrons. However, because the stability of the ion is much greater than would be expected for either a simple acid-base or charge-transfer complex, it is postulated that unshared d electrons from the metal participate in the bonding. This is symbolized by the dashed arrow in 11b, which stands for donation of d electrons into the tt orbital of the double bond or, as it is often called, back bonding. Perhaps most simple is 11c, where the C-Pt bonding is formulated as a three-... [Pg.1509]

A description involving two extreme bonding formulations is currently used to explain the nature of the M—N—O linkage in most mononuclear complexes. In the sense of formal oxidation state it is now customary to think of linear nitrosyls as derived from NO+ and bent (120°) nitrosyls as derived from NO-.23,24 Bond formation between free nitric oxide and a transition metal ion must then be considered to involve either prior donation of an electron from NO (giving NO+) or prior acceptance of an electron by NO (giving NO-) 25 in each case this would of course be followed by lone pair donation from the nitrogen. Using this somewhat simplistic view it is easy to explain the... [Pg.102]

Broadly, then, if the substitution site is primary, and therefore access to it is not hindered sterically, the nucleophile approaches it and, by donation of its electron pair, forms a partial bond to. carbon while the leaving-group—carbon bond begins to break (Equation 4.7). At the transition state, both bonds partially... [Pg.172]


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See also in sourсe #XX -- [ Pg.4 ]




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Donation, of electrons

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