Bond-line drawings showing reactions with

In the representations overleaf, you can see the line drawing and the version with methyls that stresses the bond ends. Both are satisfactory. When we wish to consider the reactivity of the double bond, and perhaps want to show that reaction occurs irrespective of the alkyl groups attached to the double bond, we put in the abbreviation R (see below), or usually just omit them. When we omit the attached groups, it helps to show what we mean by using wavy lines across the bonds, but in our urge to proceed we tend to omit even these indicators. This may... 

A fourth of many possible drawings, 3.19, is a different reaction, with the dashed line on the left at the back indicating that the upper lobe on C-2 is turning downwards to overlap with the lower lobe on C-3. This is not what happens—if it were to happen, it would produce a trans double bond in the cyclohexene product. Not only is that impossible for steric reasons, it is also forbidden, as the sum shows—there are two (4q+2)s components. We see from the three drawings 3.15, 3.17, and 3.18 that there is considerable latitude in how to place the dashed lines to identify developing overlap, but they must identify the overlap that is actually developing, just as all three... 

Electron flow paths are written in the language of Lewis dot structures and curved arrows. Lewis dot structures are used to keep track of all electrons, and curved arrows are used to symbolize electron movement. You must be able to draw a proper Lewis structure complete with formal charges accurately and quickly. Your command of curved arrows must also be automatic. These two points cannot be overemphasized, since all explanations of reactions will be expressed in the language of Lewis structures and curved arrows. A Lewis structure contains the proper number of electrons, the correct distribution of those electrons over the atoms, and the correct formal charge. We will show all valence electrons lone pairs are shown as darkened dots and bonds by lines. 

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