Chem 225 Lecture 7 Summed up summary
Chem 225 Lecture 7 Summed up summary CHEM 225
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This 3 page Class Notes was uploaded by MelLem on Tuesday February 16, 2016. The Class Notes belongs to CHEM 225 at Simmons College taught by Professor gurney in Spring 2016. Since its upload, it has received 47 views. For similar materials see Organic chemistry 2 in Chemistry at Simmons College.
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Date Created: 02/16/16
CHEM 225 Organic Chemistry II – Unit 2 – Aromatic Chemistry -‐ Lecture 7 Notes Lecture Summary: Hybridization: Sp2 and sp3 review Sp3 – • Tetrahedral (non-‐planar) • 4 steric groups attached • 109 degree “ish” angles • sigma bonds sp2 – • trigonal planar • 3 steric groups attached • 120 degree angles • pi bonds and sigma bonds everything must be in the plane when it is aromatic Common Aromatic Names: • Benzene • Toluene • Phenol • Xylene • Analine • Anisole • Benzophenone • Acetophenone Describing the relationship between substituents: If there is only 2 substituents, these names can be used to describe the relative position on the aromatic ring. • Ortho 1,2-‐disubstituted • Meta 1,3-‐disubsubstitued • Para 1,4-‐ substituted Aromatics Reactivity: • Very stable • Very unreactive Three requirements to be Aromatic: • Must be a continuous ring • All atoms in ring must be sp2 hybridized • Must fall in 4n + 2 e-‐ rule. (2, 6, 10, 14 e-‐) Aromatic? Check 1 Check 2 Check last Aromatic Ring -‐All atoms are sp2 4n + 2 e-‐ -‐planar Anti-‐aromatic Ring -‐Sp2 atoms 4ne-‐ -‐not planar Nonaromatic Breaks any rule Breaks any rule e-‐ do no matter Energy: • Aromatics are highly stable • Non aromatics have stability like regular molecules • Anti-‐aromatics are extremely unstable Aromatics are the most stable – the list is in order from highest energy stability to the lowest. When deciding aromaticity, what do you do with hetero atoms? • Heteroatoms o Sulfur – S o Oxygen – O o Nitrogen – N • When a hetero atom is singly bound, count 1 pair of electrons in the pi system (ex A) • If the hetero atom is doubly bound, do not count the lone pair. • If lone pairs can be used to achieve aromaticity driving force is great enough for atoms to hybridize. Reactivity of aromatic compounds: Oxidation Methods: Benzene – no reaction occurs when attempted to be oxidized. Toluene – will react when oxidized to form a carboxylic acid at the benzylic carbon. 1-‐ethylbenzene – will react when oxidized to form a carboxylic acid + CO2 for every additional carbon on the chain. Ethyl will produce 1 mol of CO2. Oxidation reagents for Benzene: KMnO4 / Heat, OH ▯ CrO3 ▯ Na2Cr2O7 / H2SO4, H2O ▯ Reduction: Benzene – when reduced, will not react unless under certain conditions. Birch Reduction Na(metal) CH3OH / NH3 ▯ Benzene with an e-‐ withdrawing group will react with a birch reduction agent to form a molecule with 2 double bonds para (1,4) to one another. The e-‐ withdrawing group will gain a hydrogen. Benzene with Br / light ▯ NR Toluene will react with NBS/light ▯ Br is added to the benzylic carbon as long as there is a hydrogen there that can be replaced.