Introduction to Heterocyclic Chemistry 15 + Equatorial 1-ter-butylpiperidine (ii)If the methyl group of 2-methoxy-4-methyltetrahydropyran resides in an equatorial site (of course,it is larger than hydrogen!), it then follows that the trans methoxy group at C-2 is axially ori- entated.In this arrangement there are also reinforcing anomeri interactions involving a lone pair from each oxygen atom Consequently,this conformation is favoured,by a ratio of 98:2 over the alternative in which the methyl group is axial and the methoxy group is equatorial: Me Me ans-2-Methoxy-4-methy Summary of Key Points 1.Planar cyclic polyenes containing (4n+2)R-electrons obey Huckel's rule for aromaticity and show greater stability than that predicted from their classical structures. 2.The replacement of a CH group by an atom,such as N.O or S,also leads to aromatic heterocycles. 3.Although the conformations of heterocycles are governed by the tional factors,such as the anomeric effect,can have a significant influence upon the energies of the isomers in equilibrium.Introduction to Heterocyclic Chemistry 15