I. Weakening of electron resonance donation abilityII. Benzene and its structural and chemical propertiesIII. Predicting reactions of benzeneIV. NomenclatureI. Nomenclature of Benzene SubstituentsII. Electrophilic Addition Reactions involving BenzeneIII. Further Reactions to Know Involving BenzeneI. Nomenclature of Benzene Substituentsa. When you have a common-base name (i.e. Phenol, Toluene) AND one other substituent, you use the following in the name:i. Ortha: substituent is ADJACENT to the carbon bearing the defining R groupii. Meta: substituent is 2 carbons away from the carbon bearing the R groupiii. Para: substituent is 3 carbons away from the carbon bearing the R group (OPPOSITE)b. R group that defines phenol is a hydroxyl group. R group that defines a toluene is a methyl group.i. Any additional substituents on that benzene bearing the defining R group are described as being ortha, meta, or para to the R group. And the whole name includes “ortha,” or just “o.”o-ethyltolueneII. Electrophilic Addition Reactions involving Benzenea. Normal alkene and E-X (generic electrophilic addition reagent) will result in an addition reactioni. E and X are added to substrateb. Benzene ring and E-X will be a reversible reaction, because a non-aromatic is formed from the addition of E and X on one of the alternating pi bonds of benzenei. The “would be” product cannot be isolated because the reaction is too endothermic.ii. RECALL that benzene has unusual stability, and any reaction that goes from low energy to high energy is not going to be favorable, especially for benzene given its aromatic stabilization.1. Reaction is NOT thermodynamically favorable because you start with an aromatic, and end with a non-aromatic.c. Benzene can react in an electrophilic SUBSTITUTION reaction.i. Benzene + E-X (under special conditions) will result in a benzene ring where one original Hydrogen becomes substituted by E (electrophile), and side product is H-X.1. This reaction IS thermodynamically favorable because you start with an aromatic and end with an aromatic.ii. RECALL that an electrophile is a positive charged atom/molecule; it WANTS electron densityd. The Mechanism for the Electrophilic Addition reaction using E-X (generic electrophilic addition reagent)i. Step 1: electron rich pi bond in benzene ring attacks positively charged electrophile. Electrons from pi bond from new single bond from benzene C and E, leaving behind an adjacent C without that pair of electrons, thus forming a CARBOCATION1. Because you have formed a carbocation, this is the rate determining step (R.D.S.)2. In forming this intermediate, you have gone from an aromatic to a non-aromatic.3. This carbocation intermediate is RESONANT STABILIZED: 3 resonant structures occura. Draw the electron pushing mechanism to prove thisii. Step 2: The negatively charged X- (formed from the dissociation of E-X in step 1), DE-PROTONATES the Hydrogen bonded to the C bearing the electrophile, allowing those electrons to regain their position, ending up with an aromatic.1. The X- base can de-protonate the sp3 C ONLY!III. Further reactions to know involving Benzene:a. Benzene stirred in sulfuric acid, H2SO4, has NO OBSERVABLE REACTION.i. If you take instead D2SO4 inexcess, as a source of “naked proton” (H+), with heat and time, a reaction does occur.1. All original H’s are replaced by Deuterium.2. This reaction occurs in multiple steps, specifically 6 for the replacement of each original H with Deuterium.b. Halogenation of Benzene:i. If you take benzene and Br2, no reaction occurs. You NEEDACATALYST!1. Catalyst: FeBr3 OR FeCl3a. These catalysts work with their corresponding halogen (i.e. FeBr3 with Br2)i. FeI3/I2 is too endothermic too allow reactionii. FeF3/F3 is too exothermic and is NEVER used.ii. The Mechanism: enticing benzene to attack an electrophile:1. Step 1: MAKE the ELECTROPHILE! (Important for synthesis)a. Lone pairs of one of the Bromines in Br – Br attacks Fe in FeBr3. Forming: Br – Br – FeBr3i. Fe has positive charge, Br has negative charge. The terminal Br is mildly electrophilic through induction.b. You have formed the electrophile2. Step 2: Which Br will the benzene attack?a. Benzene attacks the terminal Br because in doing so, the middle Br gains back its lone pair.iii. Nitration of Benzene:1. Overall reaction: Benzene ring is the substrate, HNO3 along with H2SO4 (both needed) to form benzene with NO2 substituent.a. Further reduction does occur, however, to form an amino group substituent.2. For this reaction, you must make an electrophile. That electrophile being: Nitronium Iona. HO – N (double bonded to O)– O-i. Nitric acidb. To make it an electrophile, protonate one of the oxygens. You must protonate the oxygen bonded to H, because then it will have a positive charge (bonded to three atoms) and thus become an electrophile.c. Then you need a very strong acid (H2SO4, NOT HCl because HCl will not protonate nitric acid)i. Sulfuric acid acts as a base (donates its proton to the oxygen – source of naked proton)d. Water then becomes a good leaving group, and breaks from NO2 following protonation, forming NO2+ in solution (along with water and HSO4- )i. Nitronium ion formed. You have your electrophilee. Pi electrons in benzene rings attack positive charge on nitrogen, forming a carbocation.f. NOTE*** Dr. Huston did not have time to finish discussing this reaction; to be continued.CHEM 0320 1st Edition Lecture 7Outline of Last Lecture I. Weakening of electron resonance donation ability II. Benzene and its structural and chemical properties III. Predicting reactions of benzene IV. Nomenclature Outline of Current Lecture I. Nomenclature of Benzene Substituents II. Electrophilic Addition Reactions involving Benzene III. Further Reactions to Know Involving Benzene Current LectureI. Nomenclature of Benzene Substituentsa. When you have a common-base name (i.e. Phenol, Toluene) AND one other substituent, you use the following in the name: i. Ortha: substituent is ADJACENT to the carbon bearing the defining R group ii. Meta: substituent is 2 carbons away from the carbon bearing the R group iii. Para: substituent is 3 carbons away from the carbon bearing the R group (OPPOSITE) b. R group that defines phenol is a hydroxyl group. R group that defines a toluene is a methyl group. i. Any additional substituents on that benzene bearing the defining R group are described as being ortha, meta, or