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Rules for bonding

Isomeric effect—The additivity rule for bond energies applies only to compounds in a homologous series and small changes in structure cause deviations in the heats of formation. If the additivity rule were correct, saturated hydrocarbons possessing the same number of carbon and hydrogen atoms would have identical heats of formation. This, however, is not correct as is shown in Table CIX, where the experimental data indicate that the heat of formation... [Pg.243]

A rule in EROS consists of a global part describing the name, reactors, phases, and kinetics and a reaction part that defines one or more reaction rules. An example of a simple EROS rule for bond formation and cleavage in Tcl looks as follows ... [Pg.233]

Corey s analysis to) of polycyclic systems and strategic bond disconnections directed by maximizing simplification of intermediates is an example of the definition of new heuristics for skeletal dissection ( 6). This analysis directs the selection of particular bonds for construction. His rules also derive in part from stereochemical considerations ( 7). A further treatment of rules for bond selection via stereochemistry would be valuable. [Pg.64]

MMe2Cl2 M = Ti-Hf. Bent s rule for bond angles 590 [ ]2- M = Ti-Hf. Non-octahedral 591... [Pg.268]

All four sp orbitals are of equal energy Therefore according to Hund s rule (Sec tion 1 1) the four valence electrons of carbon are distributed equally among them making four half filled orbitals available for bonding... [Pg.64]

The substituent groups on the double bonds of most alkenes are of course more com plicated than m this example The rules for ranking substituents especially alkyl groups are described m Table 5 1... [Pg.194]

In naming alkynes the usual lUPAC rules for hydrocarbons are followed and the suffix ane is replaced by yne Both acetylene and ethyne are acceptable lUPAC names for HC=CH The position of the triple bond along the chain is specified by number m a manner analogous to alkene nomenclature... [Pg.364]

The oxygen m furan has two unshared electron pairs (Figure 11 16c) One pair is like the pair m pyrrole occupying a p orbital and contributing two electrons to complete the SIX TT electron requirement for aromatic stabilization The other electron pair m furan IS an extra pair not needed to satisfy the 4n + 2 rule for aromaticity and occupies an sp hybridized orbital like the unshared pair m pyridine The bonding m thiophene is similar to that of furan... [Pg.463]

Kekule structure (Section 112) Structural formula for an aro matic compound that satisfies the customary rules of bond mg and is usually characterized by a pattern of alternating single and double bonds There are two Kekule formula tions for benzene... [Pg.1287]

More complete interpretations of Diels-Alder regioselectivity have been developed. MO results can be analyzed from an electrostatic perspective by calculating potentials at the various atoms in the diene and dienophile. These results give a more quantitatively accurate estimate of the substituent effects. Diels-Alder regioselectivity can also be accounted for in terms of HSAB theory (see Section 1.2.3). The expectation would be that the most polarizable (softest) atoms would lead to bond formation and that regioselectivity would reflect the best mateh between the diene and dienophile termini. These ideas have been applied using 3-2IG computations. The results are in agreement with the ortho rule for normal-electron-demand Diels-Alder reactions. ... [Pg.645]

Beryllium forms a series of cyclopentadienyl complexes [Beftj -CsHiY] with Y = H, Cl, Br, Me, —C=CH and BH4, all of which show the expected C5, symmetry (Fig. 5.10a). If the pe/ifo/topfo-cyclopentadienyl group (p. 937) contributes 5 electrons to the bonding, then these are all 8-electron Be complexes consistent with the octet rule for elements of the first short... [Pg.130]

In a formal sense, isoindole can be regarde,d as a IOtt- electron system and, as such, complies vith the Hiickel (4w- -2) rule for aromatic stabilization, with the usual implicit assumption that the crossing bond (8, 9 in 1) represents a relatively small perturbation of the monocyclic, conjugated system. The question in more explicit terms is whether isoindole possesses aromatic stabilization in excess of that exhibited by pyrrole. [Pg.114]

For the formation of the new double bond, the general rules for eliminations do apply. Following Bredt s rule, no double bond to a bridgehead carbon atom will be formed. If the elimination can lead to a conjugated system of unsaturated groups, this pathway will be favored. Otherwise the Hofmann rule will be followed, which favors an elimination towards the less substituted carbon center. [Pg.107]

Alkyne nomenclature follows the general rules for hydrocarbons discussed in Sections 3.4 and 6.3. The suffix -yne is used, and the position of the triple bond is indicated by giving the number of the first alkyne carbon in the... [Pg.259]

What do molecular orbitals and their nodes have to do with pericyclic reactions The answer is, everything. According to a series of rules formulated in the mid-1960s by JR. B. Woodward and Roald Hoffmann, a pericyclic reaction can take place only if the symmetries of the reactant MOs are the same as the symmetries of the product MOs. In other words, the lobes of reactant MOs must be of the correct algebraic sign for bonding to occur in the transition state leading to product. [Pg.1179]

Cahn-Ingold-Prelog sequence rules (Sections 6.5, 9.5) A series of rules for assigning relative priorities to substituent groups on a double-bond carbon atom or on a chirality center. [Pg.1237]

In the hydrogen bond we find the hydrogen atom attached to two other atoms. Yet our bonding rules tell us that the hydrogen atom, with only the Is orbital for bond formation, cannot form two covalent bonds. We must seek an explanation of this second bond. [Pg.316]

Both of these structures satisfy the formal valence rules for carbon, but each has a serious fault. Each structure shows three of the carbon-carbon bonds as double bonds, and three are shown as single bonds. There is a wealth of experimental evidence to indicate that this is not true. Any one of the six carbon-carbon bonds in benzene is. the same as any other. Apparently the fourth bond of each carbon atom is shared equally with each adjacent carbon. This makes it difficult to represent the bonding in benzene by our usual line drawings. Benzene seems to be best represented as the superposition or average of the two structures. For simplicity, chemists use either one of the structures shown in (30) usually expressed in a shorthand form (SI) omitting the hydrogen atoms ... [Pg.343]


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Essential Single and Double Bonds General Rules for Aromaticity

The 18-Electron Rule for Transition Metal Bonding

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