Double-bond compounds electronic structure

Note that these compounds are covalently bonded compounds containing only hydrogen and carbon. The differences in their strucmral formulas are apparent the alkanes have only single bonds in their structural formulas, while the alkenes have one (and only one) double bond in their structural formulas. There are different numbers of hydrogen atoms in the two analogous series. This difference is due to the octet rule that carbon must satisfy. Since one pair of carbon atoms shares a double bond, this fact reduces the number of electrons the carbons need (collectively) by two, so there are two fewer hydrogen atoms in the alkene than in the corresponding alkane. 

Each line in a structural formula represents one pair of shared electrons, but atoms can share more than one pair of electrons. When two atoms share one pair of electrons, the bond is called a single bond, and the structural formula shows a single line. When two atoms share four electrons, the bond is called a double bond, and the structural formula shows two lines between the atoms. Similarly, when two atoms share six electrons, the bond is called a triple bond, and the stmctural formula shows three lines between the atoms. Two carbon atoms can bond to each other through any of these three kinds of bonds, as the compounds in Figure illustrate. 

For compounds (2) and (3) there is no reason to question the assignment of triple bonds and a double bond, respectively. The structure of the Cr compound of type (2) has been shown in Fig. 1. The structure of (3) is shown in Fig. 4(a). Such bonds are consistent with the attainment of 18-electron configurations. 

SAMPLE SOLUTION (a) Each hydrogen contributes 1 valence electron, carbon contributes 4, and oxygen 6 for a total of 12 valence electrons. We are told that both hydrogens are bonded to carbon. Because carbon forms four bonds in its stable compounds, join carbon and oxygen by a double bond. The partial structure so generated accounts for 8 of the 12 electrons. Add the remaining four electrons to oxygen as unshared pairs to complete the structure of formaldehyde. 

When any substituent is introduced in hydrocarbon molecules to saturate double bond or triple bond, the electronic structure of molecule will be changed, thus the thermal effect of electron transfer of 1 mol atom will have some change. According to the impact of change in molecule structure, the explosion heat of explosive can be calculated based on the corresponding corrected thermochemical data of some groups and the corrected data are listed in Table 3.9. The combustion heat of CaHi,OcN compounds under constant pressure can be calculated as the following equation ... 

Benzene Ring The structure of the hydrocarbon compound benzene, CgHe- It is a six-carbon ring where all C-C bonds are equivalent and intermediate in length between single and double bonds. One electron per carbon atom (for a total of six) is delocalized. These six electrons have equal probability of being found anywhere around the ring. They reside in pi bonds which are perpendicular to the plane of the molecule. Benzene is the archetypal aromatic compound. 

We conclude that all terminal O atoms in the gaseous sulfur oxides, in the four sulfur oxy-fluorides, and in gaseous sulfuric are joined to the sulfur atom through double bonds. If Lewis structures are drawn with double S=0 bonds represented by two electron pairs, the coordination geometries of all these compounds are in accord with the VSEPR model. The sulfur atoms in all these molecules have five or six electron pairs in the valence shell. 

Although benzene contains three carbon-carbon double bonds, it has a unique arrangement of its electrons (the extra pairs of electrons are part of the overall ring structure rather than being attached to a particular pair of carbon atoms) which allow benzene to be relatively unreactive. Benzene is, however, known to be a cancer-inducing compound. 

Ethene can add on to certain metal salts it is believed that the extra electrons of the double bond can be donated to some extent an example is the compound PtCl2-C2H4 formed with platinum(II) chloride which has the structure... 

Since Stork et al. introduced as a new synthetic method the alkylation and acylation of carbonyl compounds via enamines, this class of compounds has been the subjeet of intensive studies 1-3). The exceptional physical and chemical behavior of the enamine structure can be ascribed to resonance by conjugation of the unshared pair of electrons of the nitrogen atom with the 77 electrons of the double bond ... 

The structure of the protonated enamines has been investigated by infrared spectroscopy. On protonation there is a characteristic shift of the band in the double-bond stretching region to higher frequencies by 20 to 50 cm with an increased intensity of absorption (6,13,14a). Protonated enamines also show absorption in the ultraviolet at 220-225 m/x due to the iminium structure (14b). This confirms structure 5 for these protonated enamines, because a compound having structure 4 would be expected to have only end absorption as the electrons on nitrogen would not be available for interaction with the n electrons of the double bond. 

Concerning nomenclature, fulvalene 2 and its related systems 1 and 3-6 are the parent structures of this class of heterocyclic cross-conjugated compounds. Both ring systems are numbered as shown in formula 9 (1,4,5,8-tetraazafulva-lene) beginning at the heteroatoms. Alternatively, as in the case of heptafulva-lene 10 (3,3 -diazaheptafulvalene), the numbers 1-7 and l -7 can be used.Tlie use of the name of the parent heterocycle connected by an olefinic double bond is often favored for the nomenclature of electron-rich olefines, for example, bis[3-(2,6-diisopropylphenyl)-4,5-dimethylthiazol-2-ylidene] for compound 51a (97LAR365). Similarly, azafulvalenes of type 11 and 12 can be re-... 

Resonance is an extremely useful concept that we ll return to on numerous occasions throughout the rest of this book. We ll see in Chapter 15, for instance, that the six carbon-carbon bonds in so-called aromatic compounds, such as benzene, are equivalent and that benzene is best represented as a hybrid of two resonance forms. Although an individual resonance form seems to imply that benzene has alternating single and double bonds, neither form is correct by itself. The true benzene structure is a hybrid of the two individual forms, and all six carbon-carbon bonds are equivalent. This symmetrical distribution of electrons around the molecule is evident in an electrostatic potential map. 

The anion in KRu04 has a slightly flattened tetrahedral structure (Ru-O 1.73 A). Organic-soluble salts like Pr4NRu04 are selective mild oxidants that will oxidize alcohols to carbonyl compounds but will not affect double bonds [54a]. ESR indicates that Ru04 (g = 1.93 gy = 1.98 gz = 2.06) has a compressed tetrahedral geometry with the electron in dz2 [54b]. 

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