Heterocycles - ANS cyclic organic molecule where one or more carbon atoms are replaced by heteroatoms Heteroatoms - ANS Atoms in an organic compound other than carbon and hydrogen Ex: Oxygen, Nitrogen, Sulfur Two main subgroups of heterocycles - ANS 1. aromatic 2. aliphatic (non-aromatic) Pyridine - ANS analogue of benzene where one C is replaced by N geometry of pyridine - ANS flat/ planar geometry with 120 degree bond angles atomic structure of pyridine - ANS sp2 hybridized atoms, 6 P electrons just like benzene resonance structure of pyridine - ANS Why does pyridine undergo substitution rather than addition? - ANS addition would destroy the aromaticity solubility of pyridine - ANS soluble in most organic solvents and completely soluble in water why is pyridine soluble in water? - ANS -ability of pyridine to accept hydrogen bonding interactions from water molecules d/t the lone pair of electrons on the nitrogen. - electronegative N creates a relatively strong dipole moment in the pyridine, thus making it an apolar compound overall. BP of pyridine vs benzene? why? - ANS -pyridine has a higher BP than benzene even though they have a similar weight -why? dipole/dipole forces Is pyridine an acid or base? - ANS weak base will form pyridinium salt when reacted with strong acids Two main reaction types of pyridine? - ANS 1. EAS- Electrophilic Aromatic Substitution 2. NAS- Nucleophilic Aromatic Substitution What happens in the EAS of pyridine? - ANS a hydrogen is replaced by an electrophile What conditions are needed for pyridine to undergo EAS? - ANS very slow and very harsh conditions- need very hot heat and a strong acid Why is pyridine less receptive to EAS than other molecules? - ANS ring is partially positive d/t electron withdrawal by the nitrogen
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