1.7 Structural Formulas of Organic Molecules Determining formal charges on individual atoms of Lewis structures is an impor- tant element in good"electron bookkeeping. " So much of organic chemistry can be made more understandable by keeping track of electrons that it is worth taking some time at the beginning to become proficient at the seemingly simple task of counting electrons 1.7 STRUCTURAL FORMULAS OF ORGANIC MOLECULES Table 1. 4 outlines a systematic procedure for writing Lewis structures. Notice that the cess depends on knowing not only the molecular formula, but also the order in which the atoms are attached to one another. This order of attachment is called the constitu. tion, or connectivity, of the molecule and is determined by experiment. Only rarely is Organic chemists have devised a number of shortcuts to speed the writing of struc- tural formulas. Sometimes we leave out unshared electron pairs, but only when we are sure enough in our ability to count electrons to know when they are present and when theyre not. We've already mentioned representing covalent bonds by dashes In con densed structural formulas we leave out some, many, or all of the covalent bonds and use subscripts to indicate the number of identical groups attached to a particular atom These successive levels of simplification are illustrated as shown for isopropyl alcohol rubbing alcohol”) CHICHCH C-C-H written as or condensed even further to OH H :0: H (CH3)2CHOH PROBLEM 1.12 Expand the following condensed formulas so as to show all the bonds and unshared electron pair (a) HOCH2 CH2NH2 (d)CH3 CHCI2 (e)CH3 CH3 (c)ClCH2CH2CI ()(CH3)2CHCH=O SAMPLE SoLUTION (a) The molecule contains two carbon atoms, which are nded to each other. both carbons bear two hydrogens. One carbon bears the group HO- the other is attached to-NH2 When writing the constitution of a molecule, it is not necessary to self with the spatial orientation of the atoms. there are many othe to represent the constitution shown What is important is to show quence OCCN (or its equivalent NCCO)and to have the correct number of hydrogens present on each atom. n order to locate unshared electron pairs, first count the total number valence electrons brought to the molecule by its component atoms. Each hydro- gen contributes 1, each carbon 4, nitrogen 5, and oxygen 6, for a total of 26. There are ten bonds shown, accounting for 20 electrons; therefore 6 electrons must be contained in unshared pairs. Add pairs of electrons to oxygen and nitrogen so tha their octets are complete, two unshared pairs to oxygen and one to nitrogen Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteDetermining formal charges on individual atoms of Lewis structures is an impor￾tant element in good “electron bookkeeping.” So much of organic chemistry can be made more understandable by keeping track of electrons that it is worth taking some time at the beginning to become proficient at the seemingly simple task of counting electrons. 1.7 STRUCTURAL FORMULAS OF ORGANIC MOLECULES Table 1.4 outlines a systematic procedure for writing Lewis structures. Notice that the process depends on knowing not only the molecular formula, but also the order in which the atoms are attached to one another. This order of attachment is called the constitu￾tion, or connectivity, of the molecule and is determined by experiment. Only rarely is it possible to deduce the constitution of a molecule from its molecular formula. Organic chemists have devised a number of shortcuts to speed the writing of struc￾tural formulas. Sometimes we leave out unshared electron pairs, but only when we are sure enough in 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 con￾densed structural formulas we leave out some, many, or all of the covalent bonds and use subscripts to indicate the number of identical groups attached to a particular atom. These successive levels of simplification are illustrated as shown for isopropyl alcohol (“rubbing alcohol”). PROBLEM 1.12 Expand the following condensed formulas so as to show all the bonds and unshared electron pairs. (a) HOCH2CH2NH2 (d) CH3CHCl2 (b) (CH3)3CH (e) CH3NHCH2CH3 (c) ClCH2CH2Cl (f) (CH3)2CHCHœO SAMPLE SOLUTION (a) The molecule contains two carbon atoms, which are bonded to each other. Both carbons bear two hydrogens. One carbon bears the group HO±; the other is attached to ±NH2. When writing the constitution of a molecule, it is not necessary to concern your￾self with the spatial orientation of the atoms. There are many other correct ways to represent the constitution shown. What is important is to show the sequence OCCN (or its equivalent NCCO) and to have the correct number of hydrogens present on each atom. In order to locate unshared electron pairs, first count the total number of valence electrons brought to the molecule by its component atoms. Each hydro￾gen contributes 1, each carbon 4, nitrogen 5, and oxygen 6, for a total of 26. There are ten bonds shown, accounting for 20 electrons; therefore 6 electrons must be contained in unshared pairs. Add pairs of electrons to oxygen and nitrogen so that their octets are complete, two unshared pairs to oxygen and one to nitrogen. H±O±C±C±N±H H W W H H W H W W H H±C±C±C±H written as or condensed even further to (CH3)2CHOH H W W H OH W CH3CHCH3 H W W H H W W O W H 1.7 Structural Formulas of Organic Molecules 19 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website