Carbon-skeleton formula

The alkane represented by the carbon skeleton formula has 11 carbons. The general formula for an alkane is C II2 2, and thus there are 24 hydrogens. The molecular formula is Cl 124 the condensed structural formula is CH3(CH2)9CH3. 

In all parts of this exercise we deduce the carbon skeleton on the basis of the alkane formed on hydrogenation of an alkene and then determine what carbon atoms may be connected by a double bond in that skeleton. Problems of this type are best done by using carbon skeleton formulas. 

Thujane Group (Bicyclo Q3.1. O hexane Type). Name the thujane-type bicyclic terpene hydrocarbons (bicyclo 3.1. (T] hexane type) as thujanes, thujenes, and thu-jadienes, and base these names on the recommended fixed numbering of the thujane carbon skeleton. (Formula 46, Chart 10). For those derivatives which contain (1) fewer carbon atoms than thujane, (2) the same number as, or more carbon atoms than thujane but do not have a carbon skeleton identical to that of thujane, or (3) more carbon atoms than thujane and a carbon skeleton identical to that of thujane but contain substituents such that the principle of like treatment of like things will be violated by using the thujane, thujene, and thujadiene names, use the bicyclo 3.1 (T]-hexane-type names based on systematic bicyclo numbering (Formula 43, Chart 10). 

Structures, the recommended numberings and names, and the bicyclo names of compounds belonging to the thujane group are shown in Chart 10. Reasons for the recommended fixed numbering of the thujane structure (Formula 46, Chart 10) and for the orientation shown in Chart 10 were discussed in connection with Chart 8 The recommended bicyclo numbering of the ring carbon skeleton (Formula 43, Chart 10) was discussed in connection with Chart 9. 

The recommended bicyclo numbering of the norpinane carbon skeleton (Formula 9, Chart 12) was discussed in connection with Chart 9. 

FIGURE 26.6 Some representative terpenes and related natural products. Structures are customarily depicted as carbon skeleton formulas when describing compounds of isoprenoid origin. 

Depicting Alkanes with Formulas and Models Chemists have several ways to depict organic compounds. Expanded, condensed, and carbon-skeleton formulas are easy to draw ball-and-stick and space-filling models show the actual shapes. 

The expanded formula shows each atom and bond. One type of condensed formula groups each C atom with its H atoms. Carbon-skeleton formulas show only carbon-carbon bonds and appear as zig-zag lines, often with branches. Each end or bend of a zig-zag line or branch represents a C atom attached to the number of H atoms that gives it a total of four bonds ... 

Cyclic Hydrocarbons A cyclic hydrocarbon contains one or more rings in its structure. When a straight-chain alkane (C H2 +2) forms a ring, two H atoms are lost as the C—C bond forms to join the two ends of the chain. Thus, cycloalkanes have the general formula C H2 . Cyclic hydrocarbons are often drawn with carbon-skeleton formulas, as shown at the top of Figure 15.6. Except for three-carbon rings, cycloalkanes are nonplanar. This structural feature arises from the tetrahedral shape around each C atom and the need to minimize electron repulsions between adjacent H atoms. As a result, orbital overlap of adjacent C atoms is maximized. The most stable form of cyclohexane, called the chair conformation, is shown in Figure 15.6D. 

FOLLOW-UP PROBLEM 15.2 Draw condensed formulas for the following compounds (a) 3-ethyl-3-methyloctane (b) I-ethyl-3-propylcyclohexane (also draw a carbon-skeleton formula for this compound) (c) 3,3-diethyl-1-hexyne (d) ina s-3-methyl-3-heptene. 

The structural formula shows all of the carbon and hydrogen atoms in the molecnle and how they are bonded together. The condensed structural formula gronps the hydrogen atoms with the carbon atom to which they are bonded. Condensed stractuial foimnlas may show some of the bonds (as the previous examples do) or none at aU. The condensed structural formula for butane can also be written as CH3CH2CH2CH3. The carbon skeleton formula (also called a line formula) shows the carbon-carbon bonds only as lines. Each end or bend of a line represents a carbon atom bonded to as many hydrogen atoms as necessary to form a total of four bonds. Carbon skeleton formnlas allow us to draw complex structures quickly. 

Write the structural formulas and carbon skeleton formulas for the five isomers of CgHi4 (hexane). 

Write the carbon skeleton formulas by using lines to represent each carbon-carbon bond. Remember that each end or bend represents a carbon atom. 

Explain the differences between a structural formula, a condensed structural formula, a carbon skeleton formula, a ball-and-stick model, and a space-filling model. 

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