Organic Chemistry Aromatic compounds chapter 17 and 18 study guide
Organic Chemistry Aromatic compounds chapter 17 and 18 study guide Chem 372
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This 5 page Study Guide was uploaded by Rachel Taylor on Friday February 26, 2016. The Study Guide belongs to Chem 372 at Eastern Michigan University taught by Dr. Friebe in Winter 2016. Since its upload, it has received 42 views. For similar materials see Organic Chemistry in Chemistry at Eastern Michigan University.
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Date Created: 02/26/16
Chapter 17: Aromatic rings and Benzene Rings Benzene rings Simplest aromatic compound; shares many characteristics of aromatic compounds Do not undergo addition reactions Br2substitutes an H with a Br in the presence of a Lewis Acid (FeBr3) Pi Bonds alternate, however equilibrium does not exist because a resonance structure is a better representation (otherwise the double bonds would be shorter than the single bonds, however the bonds are all the same length) Normally pi bonds are shorter than sigma bonds so we would end up with a shape like this, however, measurements show that the bonds are all 139 pm so there must be something else going on. This is a better representation of the bonds because there is no equilibrium, however, it is drawn with alternating bonds to keep track of the pi bonds Benzene is completely conjugated, and all the bonds are in one plane (s2 trigonal planar, 120˚ bond angles) Benzene reacts with electrophiles Nomenclature Name substituent, add “Benzene” Groups: Ortho: Meta: Para: Common roots (assign the number 1 to the common root substituent) Phenol: Toluene: Aniline: Benzene can be abbreviated as PhH Phenol can be abbreviated as PhOH Then benzene isn’t the longest chain, it is a group: Benzyl: Phenyl: Aryl (Aromatic derivatives): Aromatic rules MUST be: Cyclic, Planar, completely conjugated (all atoms must participate in pi bonding), and follow Hückel’s rule (4n+2=# of π electrons). Examples: 3 2 π e - 6 π e- 6 π e- 10 π e - 18 π e- n=0 n=1 n=1 n=2 n=4 Note: Not all poly cyclic aromatic compounds like #4 above follow Hückel’s rule. Anti-aromatic compounds are extremely unstable and they have 4n π electrons Examples: Both have 4 electrons where n=1 Non-aromatic compounds do not satisfy one or more of the four rules Examples: not completely not planar not cyclic not planar conjugated Practice: Draw an aromatic compound with a triple bond Chapter 18: Reactions with aromatic compounds Due to the higher stability of an aromatic compound, pi bonds associated with them do not break in addition reactions like typical double and triple bonds. Only undergoes substitution reactions via Sn1 (see notes on Sn1, Sn2, E1 and E2 reactions). Types of substitutions Halogenation: X ,2FeX =3 Nitration: HNO ,3H S2 =>4 Sulfonation: SO ,3H 2O =4 Friedel- Crafts alkylation: RCl, AlC3 => Friedel- Crafts acylation: RCOCl, AlCl3=> Activators and deactivators Activators activate benzene rings by donating electrons to the rings. The electrons stabilize the carbocation intermediate. Deactivators have a partial or full positive charge. This deactivates the ring by creating an unstable carbocation. Deactivators undergo reactions more slowly than activators Ortho/Para directors and Meta directors Ortho/Para directors are all activators and halogens are Ortho/Para directors. Meta directors are all deactivators except halogens. Most activating groups (Electron donating) NH , NHR, NR 2 2 -OH -OR - -NHCOR Activating Ortho/Para Directors -R Ortho/Para Directors and Deactivators -F, -Cl, -Br, -I Deactivating Meta Directors CHO COR COOR COOH CN SO H 3 NO 2 Most Deactivating groups (electron N R 3 withdrawing)
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