Molecule skeletal structures

Isoprene (2-methylbuta- 1,3-diene [Structures 7.1a and 7.1b]) is a C5 unit. Structure 7.1a shows the full structural formula where each line between the atoms represents two shared electrons in a covalent bond. In the case of more complex molecules, skeletal structures are used, as in Structure lb, where carbon atoms are normally represented by an intersection of bonds. Carbon-hydrogen bonds are not shown, although all other atoms (O, N, P and so on) are indicated. 

In skeletal structures, the carbon and hydrogen atoms are not shown, and the bonds to hydrogen are usually also not shown (although the hydrogen atoms within the functional groups, e.g. alcohols, amines, aldehydes and carboxylic acids, are shown). All other atoms are written. These structures are the most useful (and recommended for use by the reader) because they are uncluttered and quickly drawn, whilst showing all of the important parts of the molecule. Skeletal structures are usually drawn to indicate the approximate shape of the molecule, which is determined by the hybridisation of the atoms (see Section 1.5). 

Determine the geometry about each interior atom in each molecule and sketch the molecule. (Skeletal structure is indicated in parentheses.)... 

Organic molecules are usually drawn using either condensed structures or skeletal structures. In condensed structures, carbon-carbon and carbon-hydrogen bonds aren t shown. In skeletal structures, only the bonds and not the atoms are shown. A carbon atom is assumed to be at the ends and at the junctions of lines (bonds), and the correct number of hydrogens is menially supplied. 

B There are a total of sixteen valence electrons in the cyanamide molecule (five from each nitrogen atom, four from carbon and one electron from each hydrogen atom). The formula has been written as NH2CN to remind us that carbon, the most electropositive p-block element in the compound should be selected as the central atom in the skeletal structure. 

A The skeletal structure for SO2 has two terminal oxygen atoms bonded to a central sulfur atom. Sulfur has been selected as the central atom by virtue of it being the most electropositive atom in the molecule. It turns out that two different Lewis structures of... 

Pulsed FT-NMR has facilitated the study of nuclei other than H where the sensitivity obtainable from a CW instrument is totally inadequate. In particular, 13C NMR, the sensitivity of which is nearly 10-4 less than that of the proton (Table 9.9), is now a well-established technique that yields information on the skeletal structure of complex molecules. The pulsed technique also enables proton spectra to be obtained from samples as small as a few micrograms. 

Skeletal structural formulae are commonly used, particularly for large molecules, because they are easily drawn and the functional groups are clearly shown. 

An important mechanistic question is the structure of the C3H5N product generated in the C2H4 elimination reaction. One possibility would be to simply lose C2H4, which would retain the aza-bicyclobutane skeletal structure. This is rather unlikely, since this simple aza-bicyclobutane molecule is substantially less stable [25] than the ethyl derivative studied. 

In naming non-linear homopolymer molecules, the italicized prefix for the skeletal structure of the macromolecule is placed before the source-based name of the constituent linear chain. 

In naming non-linear copolymer molecules comprising linear subchains of the same monomeric units in a single type of skeletal structure, the italicized prefix for the skeletal structure is placed before the source-based name of the constituent linear subchains. In the case of star macromolecules with block copolymer arms, the block named first after the prefix emanates from the branch point. 

In naming non-linear copolymer molecules having linear subchains of two or more types, the italicized connective for the skeletal structure is placed between the source-based names of the types of constituent linear subchains. In the case of branched and comb-like macromolecules, the linear chain named before the connective is that which forms the main chain, whereas that (those) named after the connective forms (form) the side-chain(s). The names of different species of side-chain are separated by semicolons. In the case of variegated star macromolecules the prefix is placed before the name of the macromolecule with the different species of arms separated by semicolons. 

Most of the subsequent chapters in this book use simple line structures or skeletal structures to represent molecules, as was done in Chapters 1 and 2. However, you should always have in mind the model that is presented in this chapter so that you can call on it whenever a better picture for bonding is needed to explain an observation. 

A complete structural formula (such as a Lewis structure) shows all the atoms and bonds in the molecule. A condensed structural formula shows each central atom along with the atoms bonded to it. A line-angle formula (sometimes called a skeletal structure or stick figure)... 

The degradation work had up to this point occupied itself mainly with the proof of the gross skeletal structure, and relatively little attention had been given to the stereochemistry of the molecule. It was at this point that this aspect of the problem was cleared by the determination of the structure of strychnine by X-ray crystallographic analysis independently by Robertson and Beevers (35) and Bijvoet et al. (36). 

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