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CHAP. 18]                           ORGANIC CHEMISTRY                                 263


               formulas or graphical formulas. The structural formulas for compounds (a)to(e) described in Example 18.1
               may be written as follows:
                                     H                   H                       H

                             (a)  H  C   H       (b) H   C   O   H       (c)  H   C  N   H
                                     H                   H                        H   H

                                              H

                                     (d)  H   C   O       (e)  F   C  C   F

                   As the number of carbon atoms per molecule increases, the structures are written with significantly less
               effort using condensed formulas rather than structural formulas. Condensed formulas are like structural formulas
               except that in a condensed formula, the hydrogen atoms are written to the right of the larger atom to which
               they are attached. (Since it can form only one bond, a hydrogen atom cannot be attached to another hydrogen
               atom and still be part of the organic molecule.) For example, a molecule with a carbon atom connected (1) to
               a nitrogen atom bonded to two hydrogen atoms and also (2) to three other carbon atoms, each bonded to three
               hydrogen atoms, may be represented as

                                                           CH 3
                                                     CH 3  C   NH 2

                                                           CH 3

               To see the efficiency of this representation, write out both this condensed formula and the structural formula for
               this compound and compare the effort that it takes.
                   For even greater convenience in representing the structures of organic compounds, particularly in printed
               material, line formulas are used, so-called because they are printed on one line. In line formulas, the symbol for
               each carbon atom is written on a line adjacent to the symbols for the other elements to which it is bonded. Line
               formulas show the general sequence in which the carbon atoms are attached, but to interpret them properly, the
               permitted total bond orders for all the respective atoms must be kept in mind. Again referring to compounds
               (a)to(e) described in Example 18.1, the line formulas are as follows:
                     (a)  CH 4   (b) CH 3 OH    (c) CH 3 NH 2  (d)  CH 2 O   (e)  CF  CF or FC  CF

               If the permitted total bond orders of the respective atoms are remembered, it is apparent that the line formula
               CH 4 cannot represent such structures as
                                               H  C   H   H     (incorrect)

                                                  H

               which has a total order of 2 for one of the hydrogen atoms and a total bond order of only 3 for the carbon atom.
               Similarly, the formula CH 2 O cannot represent the structure H C O HorH C O H, because in either of
               these cases, the total bond order of the carbon atom is less than 4 and in H C O H the total bond order of
               the oxygen is greater than 2. Accordingly, line formulas must be interpreted in terms of the permitted total bond
               orders.

               EXAMPLE 18.2. Write structural and condensed formulas for the molecules represented by the following formulas:
               (a)C 2 H 4 and (b)CH 3 COCH 3 .
                Ans.  (a) Since the hydrogen atoms can have only a total bond order of 1, the two carbon atoms must be linked together.
                         In order for each carbon atom to have a total bond order of 4, the two carbon atoms must be linked to each
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