CHAPTER ELEVEN Arenes and Aromaticity alkynes, however, benzene proved to be inert. Benzene does react with Br2 in the pres ence of iron(im) bromide as a catalyst, but even then addition isnt observed Substitu- tion occurs instead no observable reaction Bromobenzene Hydrogen bromide Furthermore, only one monobromination product of benzene was ever obtained, which suggests that all the hydrogen atoms of benzene are equivalent. Substitution of one hydrogen by bromine gives the same product as substitution of any of the other hydrogens Chemists came to regard the six carbon atoms of benzene as a fundamental struc tural unit. Reactions could be carried out that altered its substituents, but the integrity of he benzene unit remained undisturbed. There must be something"special"about ben- zene that makes it inert to many of the reagents that add to alkenes and alkynes In 1866, only a few years after publishing his ideas concerning what we now rec- ognize as the structural theory of organic chemistry, August Kekule applied it to the structure of benzene. He based his reasoning on three premises 1. Benzene is Cah 2. All the hydrogens of benzene are equivalent. 3. The structural theory requires that there be four bonds to each carbon Kekule advanced the venturesome notion that the six carbon atoms of benzene were oschmidt, who was later to joined together in a ring. Four bonds to each carbon could be accommodated by a sys tem of alternating single and double bonds with one hydrogen on each carbon University of Vienna, pri- ining a structural formula for benzene similar to that H five years later. Loschmidt's ook reached few readers d his ideas were not well known H an you write? An article in a flaw in Kekule s structure for benzene was soon discovered. Kekule's structure the March 1994 issue of the quires that 1, 2-and 1, 6-disubstitution patterns create different compounds (isomers) Journal of Chemical Educa- ion(pp 222-224)claims ed and draws structural formulas for 25 of them 1. 2-Disubstituted 1.6-Disubstituted derivative of benzene derivative of benzene The two substituted carbons are connected by a double bond in one but by a single bond in the other. Since no such cases of isomerism in benzene derivatives were known and Back Forward Main MenuToc Study Guide ToC Student o MHHE Websitealkynes, however, benzene proved to be inert. Benzene does react with Br2 in the pres￾ence of iron(III) bromide as a catalyst, but even then addition isn’t observed. Substitu￾tion occurs instead! Furthermore, only one monobromination product of benzene was ever obtained, which suggests that all the hydrogen atoms of benzene are equivalent. Substitution of one hydrogen by bromine gives the same product as substitution of any of the other hydrogens. Chemists came to regard the six carbon atoms of benzene as a fundamental struc￾tural unit. Reactions could be carried out that altered its substituents, but the integrity of the benzene unit remained undisturbed. There must be something “special” about ben￾zene that makes it inert to many of the reagents that add to alkenes and alkynes. In 1866, only a few years after publishing his ideas concerning what we now rec￾ognize as the structural theory of organic chemistry, August Kekulé applied it to the structure of benzene. He based his reasoning on three premises: 1. Benzene is C6H6. 2. All the hydrogens of benzene are equivalent. 3. The structural theory requires that there be four bonds to each carbon. Kekulé advanced the venturesome notion that the six carbon atoms of benzene were joined together in a ring. Four bonds to each carbon could be accommodated by a sys￾tem of alternating single and double bonds with one hydrogen on each carbon. A flaw in Kekulé’s structure for benzene was soon discovered. Kekulé’s structure requires that 1,2- and 1,6-disubstitution patterns create different compounds (isomers). The two substituted carbons are connected by a double bond in one but by a single bond in the other. Since no such cases of isomerism in benzene derivatives were known, and X X 1 4 2 3 6 5 1,2-Disubstituted derivative of benzene X X 1 4 2 3 6 5 1,6-Disubstituted derivative of benzene C C H C C H C C H H 1 2 3 4 6 5 H H C6H6 Benzene Br2 Bromine CCl4 FeBr3 no observable reaction C6H5Br Bromobenzene HBr Hydrogen bromide 400 CHAPTER ELEVEN Arenes and Aromaticity In 1861, Johann Josef Loschmidt, who was later to become a professor at the University of Vienna, pri￾vately published a book con￾taining a structural formula for benzene similar to that which Kekulé would propose five years later. Loschmidt’s book reached few readers, and his ideas were not well known. How many isomers of C6H6 can you write? An article in the March 1994 issue of the Journal of Chemical Educa￾tion (pp. 222–224) claims that there are several hun￾dred and draws structural formulas for 25 of them. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website