Organic molecule bonding alkanes

What about a substance wrth the molecular formula 71414 Thrs compound can not be an alkane but may be erther a cycloalkane or an alkene because both these classes of hydrocarbons correspond to the general molecular formula C H2 Any time a ring or a double bond is present in an organic molecule its molecular formula has two fewer hydrogen atoms than that of an alkane with the same number of carbons... 

Three other all-atom force fields have also received much recent attention in the literature MMFF94 [36-40], AMBER94 [9] and OPLS-AA [41, 42] and are becoming widely used. The latter two force fields both use non-bonded parameters which have been adjusted in order to reproduce experimental liquid phase densities and heats of vaporisation of small organic molecules. For example, OPLS-AA includes calculations on alkanes, alkenes, alcohols. 

Replacement of a hydrogen atom within an organic molecule, for example an alkane, by a substituent X changes the electronic environments of directly bonded and of more remote carbon nuclei. Thereby l3C NMR signals are shifted either upheld or downfield the difference between the chemical shifts 8 of a certain carbon atom in the substituted and the unsubstituted parent compound is called the substituent effect. For this term the abbreviation SCS (substituent-induced chemical shift) has generally been adopted in the literature and will also be used here. The SCS is given by the equation... 

Why are there so many organic compounds The answer is that a relatively small number of atoms can bond together in a great many ways. Take molecules that contain only carbon and hydrogen (hydrocarbons) and have only single bonds. Such compounds belong to the family of organic molecules called saturated hydrocarbons, or alkanes. 

Most organic compounds can be derived from alkanes. In addition, many important parts of organic molecules contain one or more alkane groups, minus a hydrogen atom, bonded as substituents onto the basic organic molecule. As a consequence of these factors, the names of many organic compounds are based on alkanes. It is useful to know the names of some of the more common alkanes and substituent groups derived from them, as shown in Table 1.3. 

Alkanes are the world s most abundant organic resource. Olefins, by contrast, are relatively scarce they are, however, the most important class of intermediate in the commodity chemical industry [1], Thus the ability to convert alkanes to alkenes is a reaction with tremendous potential utility. Likewise, in view of the obvious importance of the carbon-carbon double bond functionality in the synthesis of complex organic molecules, the ability to introduce unsaturation into unfunctionalized alkyl groups is also a very alluring goal. 

Definition A functional group refers to that portion of an organic molecule that is made up of atoms other than carbon and hydrogen, or which contains bonds other than C-C and C-H bonds. For example, ethane [Following fig.(a)] is an alkane and has no functional group. All the atoms are carbon and hydrogen and all the bonds are C-C and C-H. 

Bengali AA, Arndtsen BA, Burger PM, Schultz RH, Weiller BH, Kyle KR, Moore CB, Bergman RG. Activation of carbon-hydrogen bonds in alkanes and other organic molecules by Ir(I), Rh(I), and Ir(II) complexes. Pure Appl Chem 1995 67 281-288. 

R. G. Bergman, Activation of Carbon-Hydrogen Bonds in Alkanes and Other Organic Molecules Using Organotransition Metal Complexes, Adv. Chem. Ser. 230, 211-20... 

Alkanes are organic molecules in which all the carbons are bonded to four atoms (i.e., all single bonds). These molecules are saturated because carbon has the maximum number of atoms surrounding it. Organic molecules are named systematically using a straight-chain or unbranched alkane as a backbone (see Table 12.2). 

A thoughtful reader would have noticed that, while plenty of methods are available for the reductive transformation of functionalized moieties into the parent saturated fragments, we have not referred to the reverse synthetic transformations, namely oxidative transformations of the C-H bond in hydrocarbons. This is not a fortuitous omission. The point is that the introduction of functional substituents in an alkane fragment (in a real sequence, not in the course of retrosynthetic analysis) is a problem of formidable complexity. The nature of the difficulty is not the lack of appropriate reactions - they do exist, like the classical homolytic processes, chlorination, nitration, or oxidation. However, as is typical for organic molecules, there are many C-H bonds capable of participating in these reactions in an indiscriminate fashion and the result is a problem of selective functionalization at a chosen site of the saturated hydrocarbon. At the same time, it is comparatively easy to introduce, selectively, an additional functionality at the saturated center, provided some function is already present in the molecule. Examples of this type of non-isohypsic (oxidative) transformation are given by the allylic oxidation of alkenes by Se02 into respective a,/3-unsaturated aldehydes, or a-bromination of ketones or carboxylic acids, as well as allylic bromination of alkenes with NBS (Scheme 2.64). 

In Chapter 3 we learned that a functional group contains a heteroatom or n bond and constitutes the reactive part of a molecule. Alkanes are the only family of organic molecules that have no functional group, and therefore, alkanes undergo few reactions. In fact, alkanes are inert to reaction unless forcing conditions are used. 

FIGURE 7.1 Bonding in the alkanes involves sp hybridized orbitals on carbon, (a) Methane, (b) Ethane. The orbitals shown here are typical sketches used by organic chemists to describe bonding in organic molecules. Figure 6.44 compares these shapes to the actual shapes of the hybrid orbitals. 

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