Importance of drawing structures
A structure must be given, otherwise the product of the reaction cannot be determined. The location of single, double, and triple bonds must be specified.
Types of Structures
In Lewis structures, all individual bonds are shown. Formal charge is a way of keeping track of the electrons. Formal charge is equal to [number of valence electrons] B [nonbonding electrons] B 0.5 [bonding electrons]. In condensed structural formulas, atoms are bonded to a central atom are listed after the atom. In a skeletal structure, carbon atoms are assumed to be where two lines meet or at the end of the line. Hydrogens are not shown. In a sawhorse structure, the drawing is looking down the carbon-carbon bond.
Constitutional isomers have the same formula, but different points of attachment. Configurational isomers have the same formula and the same point of attachment, but different orientation in space. Conformational isomers have the same formula and the same point of attachment, but the rotation about single bonds is different. In the eclipsed conformation of ethane, the front hydrogens block the back hydrogens. In the staggered conformation, the hydrogens are as far away from each other as possible. The staggered conformation is the most stable. For the conformations of butane, the front two carbons remain in place and the back two carbons rotate around the carbon 2 and carbon 3 bond. In the totally eclipsed conformation, one methyl blocks the other methyl. In the gauche conformation, the methyls are 60o apart. In the eclipsed conformation, the methyls are 120o apart. In the anti conformation, the methyls are 180o apart. The stability of butane is anti > gauche > eclipsed > totally eclipsed.
Me is an abbreviation for methyl, a CH3-. Et is an abbreviation for ethyl, a CH3CH2-. Pr is an abbreviation for propyl, a CH3CH2CH2-. Butyl is an abbreviation for butyl, a CH3CH2CH2CH2-. Ph is an abbreviation for phenyl, a benzene ring. Ar is an abbreviation for aromatic or aryl, a benzene ring. Ac is an abbreviation for acetyl, a methyl next to a C=O. Bz is an abbreviation for benzoyl, a benzene next to a C=O. Bn is an abbreviation for benzyl, a benzene attached to a CH2. Pyr is an abbreviation for pyridine, a six-membered ring with alternating double and single bonds and containing nitrogen.