Carbon tetravalent

Almost all stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocatiom are one such class of compounds. 

Silapharmaka often exhibit a stronger drug efficiency compared to the carbon analoga. They are derived from the latter by replacing tetravalent carbon by tetravalent silicon at the bioactive center. This is one more nice example of the analogy between tetravalent carbon and silicon. 

RG21 This is the formal reverse process of RG12, but here the valence of atom X is reduced. Obviously, this scheme should not be applied indiscriminately, (for instance to each tetravalent carbon, changing it to a carbene) since many reactions with no chemical significance would result. Care has therefore been taken in the evaluation phase to find the appropriate sites for its application. 

In the 1890s, Nef mentioned that the functional group —NC of the isocyanides contains a divalent carbon atom C° and therefore there is a large difference between their chemistry and that of the other chemical compounds that contain only tetravalent carbon atoms Any synthesis of isocyanides corresponds to a conversion of into and all chemical reactions of isocyanides correspond to transitions of the carbon atoms C into... 

Silicon s tetravalent pyramid crystalline structure, similar to tetravalent carbon, results in a great variety of compounds with many practical uses. Crystals of sihcon that have been contaminated with impurities (arsenic or boron) are used as semiconductors in the computer and electronics industries. Silicon semiconductors made possible the invention of transistors at the Bell Labs in 1947. Transistors use layers of crystals that regulate the flow of electric current. Over the past half-century, transistors have replaced the vacuum tubes in radios, TVs, and other electronic equipment that reduces both the devices size and the heat produced by the electronic devices. 

A chemical reaction Is the result of competition It Is a race that Is won by the fastest runner. A collection of molecules tend to do, by and large, what Is easiest for them. An alkyl halide with p-hydrogen atoms when reacted with a base or a nucleophile has two competing routes substitution (Sj,jl and Sj,j2) and elimination. Which route will be taken up depends upon the nature of alkyl halide, strength and size of base/nucleophile and reaction conditions. Thus, a bulkier nucleophile will prefer to act as a base and abstracts a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa. 

Both 0+ bonded to three atoms and N+ bonded to four atoms are isoelectronic with tetravalent carbon, in other words, they have a full octet of electrons. Despite the positive charge, these atoms are not electron-deficient and are unable to make a new bond with the electron-rich nucleophiles. 

Many of the intermediates in organic reactions derive their high reactivity from the fact that they involve low-valent forms of carbon that exhibit a thermodynamic drive to form a tetravalent carbon. In this connection, zero valent atomic carbon can be considered the ultimate in low valent carbon centered reactive intermediates. Much of the attraction of this fascinating species results from the fact that, in its drive to form four bonds, it often traverses other reactive species such as carbines, carbenes, and free radicals. 

The methane molecule is a very important molecule in organic chemistry, the geometry around the tetravalent carbon atom being basic to the understanding of the structure, isomerism and optical activity of a very large number of compounds. It is a tetrahedral molecule belonging to the tetrahedral point group, Td. 

In both papers two key ideas were set forth — 1) the idea of the tetravalent carbon atom, and 2) the concept of catenation (that carbon atoms could form chains). Both papers also stated explicitly, for the first time, what became known as the chemical stracture of a compound, and the idea that the properties of the compoimds depended on the properties and arrangement of their component atoms, rather than the more complex (and less well defined) radicals. The appearance of these papers also resulted in a polemical interchange over priority that left Couper a broken man, and boosted Kekule (with the help of Wurtz, amongst others) to the top echelons of organic chemistry in Emope (5). 

Abstraction of a tetravalent carbon has been seen in the abstraction by F of R from RCl Firouzbakht Fcrricri Wolf Rack J. Am. Chem. oc. 1987,109, 2213. 

In chemical shift calculations for acylium ions, it was not necessary to model the ionic lattice to obtain accurate values. These ions have tetravalent carbons with no formally empty orbitals, as verified by natural bond orbital calculations (89). Shift calculations for simple carbenium ions with formally empty orbitals may require treatment of the medium. We prepared the isopropyl cation by the adsorption of 2-bromopropane-2-13C onto frozen SbF5 at 223 K and obtained a 13C CP/MAS spectrum at 83 K (53). Analysis of the spinning sidebands yielded experimental values of = 497 ppm, 822 = 385 ppm, and (%3 = 77 ppm. The isotropic 13C shift, 320 ppm, is within 1 ppm of the value in magic acid solution (17). Other NMR evidence includes dipolar dephasing experiments and observation at higher temperature of a scalar doublet ( c-h = 165 Hz) for the cation center. 

Covalent bonds are the bonds with which we are concerned in our study of organic chemistry. The building block of structural organic chemistry is the tetravalent carbon atom. With few exceptions, carbon compounds are formed with four covalent bonds to each carbon atom, regardless of whether the combination is between two or more carbon atoms or between carbon and some other element. 

The building block of structural organic chemistry is the tetravalent carbon atom. With few exceptions, carbon compounds can be formulated with four... 

The way in which compounds with asymmetric carbon atoms are racemized is more complicated. One possibility would be for a tetrahedral chiral carbon attached to four groups to become planar and achiral without breaking any bonds. Theoretical calculations indicate that this is not a likely process for chiral tetravalent carbon but, as we will see, it does occur with chiral carbon and other chiral atoms that are attached to three groups ... 

Write three isomeric structures for C4H2 with tetravalent carbon and univalent hydrogen. Decide which isomer has the most favorable geometrical configuration and estimate the resonance energy for this isomer. 

The monovalent azide group, -N3, is closely related to the divalent diazo group and can be regarded as derived from the latter by replacement of a tetravalent carbon atom by... 

How are these reactive carbene species generated Two groups must be removed from a tetravalent carbon, leaving behind one pair of electrons. We will examine three of the more important methods that accomplish this. The first is the elimination of N2 from diazo compounds. The simplest diazo compound is diazomethane ... 

The free radicals we have studied are one class of reactive intermediates. Reactive intermediates are short-lived species that are never present in high concentrations because they react as quickly as they are formed. In most cases, reactive intermediates are fragments of molecules (like free radicals), often having atoms with unusual numbers of bonds. Some of the common reactive intermediates contain carbon atoms with only two or three bonds, compared with carbon s four bonds in its stable compounds. Such species react quickly with a variety of compounds to give more stable products with tetravalent carbon atoms. 

The phosphoranes are derivatives of the pentahydride of phosphorus, PH6, in which the five ligands are covalently bonded to phosphorus. The stereochemistry of pentavalent phosphorus relates to the trigonal bipyramid, just as that of tetravalent carbon relates to the tetrahedron. There are significant differences in the stereochemistry of the compounds of these two elements, other than isomer numbers. Some tetracoordi-nated phosphorus compounds become pentacoordinated rapidly and reversibly. Most pentacoordinated phosphorus compounds change their ligand distribution on the trigonal bipyramidal skeleton very easily by mechanisms that involve the simple deformation of bonds, rather than the rupture and re-formation of bonds. 

This alternative hybridization scheme explains how carbon can combine with four atoms in some of its compounds and with three other atoms in other compounds. You may be aware of the conventional way of depicting carbon as being tetravalent in all its compounds it is often stated that carbon always forms four bonds, but that sometimes, as in the case of ethylene, one of these may be a double bond. This concept of the multiple bond preserves the idea of tetravalent carbon while admitting the existence of molecules in which carbon is clearly combined with fewer than four other atoms. 

For example, although p a tables indicate that fert-butoxide [(CH3)3CO ] is a stronger base than ethoxide (CH3CH20 ), ethoxide is the stronger nucleophile. The three CH3 groups around the O atom of ferf-butoxide create steric hindrance, making it more difficult for this big, bulky base to attack a tetravalent carbon atom. 

K0C(CH3)3, DBU, and DBN are too sterically hindered to attack a tetravalent carbon, but are able to remove a small proton, favoring elimination over substitution. 

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