Bonds structural formulae

The physical and chemical behavior of molecules is largely determined by their constitution (the type and number of the atoms they contain and their bonding). Structural formulas can therefore be used to predict not only the chemical reactivity of a molecule, but also its size and shape, and to some extent its conformation (the spatial arrangement of the atoms). Some data providing the basis for such predictions are summarized here and on the facing page. In addition, L-dihy-droxyphenylalanine (L-dopa see p.352), is used as an example to show the way in which molecules are illustrated in this book. 

Normally a single straight line connecting the atomic symbols represents a single bond two lines represent a double bond and three lines represent a triple bond. Structural formulas of some common carbon compounds are given below. 

If the bond valence b calculated from (13.4.1) and (13.4.2) for a cluster M matches the number of connecting lines drawn between pairs of adjacent atoms in a conventional valence bond structural formula, the cluster is termed electron-precise. ... 

Valence-bond structural formulas for the dihydrogen borate ion, [BO(OH)2]-, and its measured dimensions in... 

The valence-bond structural formula of this cation is given below ... 

These are deduced from a topological picture (2D picture) of the molecules. The picture carries information on how the atoms are connected and what is the nature of bonds (structural formula of a molecule). Mathematically, the topology picture is described with the connectivity matrix. Pioneering work in this field was published in 1947 by Wiener on paraffin hydrocarbons [31]. It is defined as a half sum of the off-diagonal elements in the topological distance matrix. In the last few decades dozens of descriptors have been deduced... 

The great advantage of this style is that the basic nature of the bonding is immediately obvious. For the central atom, no more than a set of s and p orbitals are involved. Importantly, we must add that rewriting multiply bonded structural formulas in ionic form does not necessarily make them nonhypervalent. A good example is periodic acid, H5IO6, where both the traditional and newer ionic formulas are hypervalent ... 

Covalent Bonds Structural Formulas Multiple Covalent Bonds Polar Covalent Bonds... 

Organic chemists have devised a number of shortcuts to speed the writing of structural formulas Sometimes we leave out unshared electron pairs but only when we are sure enough m our ability to count electrons to know when they are present and when they re not We ve already mentioned representing covalent bonds by dashes In condensed structural formulas we leave out some many or all of the covalent bonds and use sub scripts to indicate the number of identical groups attached to a particular atom These successive levels of simplification are illustrated as shown for isopropyl alcohol ( rub bmg alcohol )... 

With practice writing structural formulas for organic molecules soon becomes rou tine and can be simplified even more For example a chain of carbon atoms can be rep resented by drawing all of the C—C bonds while omitting individual carbons The result mg structural drawings can be simplified still more by stripping away the hydrogens... 

We can relate the conformational preference for an equatorial methyl group m methylcyclohexane to the conformation of a noncyclic hydrocarbon we discussed ear her butane The red bonds m the following structural formulas trace paths through four carbons beginning at an equatorial methyl group The zigzag arrangement described by each path mimics the anti conformation of butane... 

Bond dissociation energies refer to bond indicated in structural formula for each substance... 

Write structural formulas or build molecular models and give the lUPAC names for all the alkenes of molecular formula C6H12 that contain a trisub stituted double bond (Dont forget to include stereoisomers)... 

So far we have represented cycloalkenes by structural formulas m which the double bonds are of the cis configuration If the ring is large enough however a trans... 

Wnte a structural formula or build a molecular model and give a correct lUPAC name for each alkene of molecular formula C7H14 that has a tetrasubstituted double bond... 

The free anomeric hydroxyl group IS the one shown at the far right of the preced ing structural formula The symbol is used to represent a bond of variable stereochemistry... 

Birds excrete nitrogen as uric acid Uric acid is a purine having the molecular formula C5H4N4O3 it has no C—H bonds Write a structural formula for uric acid... 

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... 

Natural rubber is composed of polymerized isoprene units. When rubber is under tension, ozone attacks the carbon-carbon double bond, breaking the bond. The broken bond leaves adjacent C = C bonds under additional stress, eventually breaking and placing shll more stress on surrounding C = C bonds. This "domino" effect can be discerned from the structural formulas in Fig. 9-4. The number of cracks and the depth of the cracks in rubber under tension are related to ambient concentrations of ozone. 

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. 

Note that there is no one-carbon alkene corresponding to methane, since hydrogen can never form more than one covalent bond, and there is no other carbon atom in the structural formula. Therefore, the first compound in the alkene series is ethene, while the corresponding two-carbon compound in the alkane series, ethane, is the second compound in the series, with methane the first. 

As in the alkanes, it is possible for carbon atoms to align themselves in different orders to form isomers. Not only is it possible for the carbon atoms to form branches which produce isomers, but it is also possible for the double bond to be situated between different carbon atoms in different compounds. This different position of the double bond also results in different structural formulas, which, of course, are isomers. Just as in the alkanes, isomers of the alkenes have different properties. The unsaturated hydrocarbons and their derivatives are more active chemically than the saturated hydrocarbons and their derivatives. 

Methane is a tetrahedral molecule its four hydrogens occupy the corners of a tetrahedron with carbon at its center. We often show three-dimensionality in structural formulas by using a solid wedge ) to depict a bond projecting from the paper toward... 

Sketch a potential energy diagram for rotation around a carbon-carbon bond in propane. Clearly identify each potential energy maximum and minimum with a structural formula that shows the conformation of propane at that point. Does your diagram more closely resemble that of ethane or of butane Would you expect the activation energy for bond rotation in propane to be more than or less than that of ethane Of butane ... 

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