RELATIVE RATES OF ELECTROPHILIC AROMATIC SUBSTITUTION

EXPERIMENT 9: RELATIVE AROMATIC SUBSTITUTION CHEM 31.1 POST-LAB

RATES

OF

ELECTROPHILIC

J.M. EGANA1 1

NATIONAL INSTITUTE OF MOLECULAR BIOLOGY AND BIOTECHNOLOGY, COLLEGE OF SCIENCE UNIVERSITY OF THE PHILIPPINES, QUEZON CITY 1101, PHILIPPINES DATE PERFORMED: 24 SEPTEMBER 2014 DATE SUBMITTED: 1 OCTOBER 2014

ANSWERS TO QUESTIONS (ATQ)

1. Arrange the compounds used in the experiment in order of increasing reactivity towards Br2 in CH3COOH. Explain. Chlorobenzene < benzene < nitrophenol < acetanilide < phenol < aniline The reactivity of these aromatic compounds is based mainly on the activating or deactivating effects of their substituent groups. The table below shows the substituent groups of the aromatic compounds used. Aromatic compound Chlorobenzene Benzene Nitrophenol Acetanilide Phenol Aniline

Substituent Groups -Cl none -OH, -NO2 -NHCOCH3 -OH -NH2

“The common characteristic of all activating groups is that they donate electrons to the ring, thereby making the ring more electron-rich, stabilizing the carbocation intermediate, and lowering the activation energy for its formation.” Thus, aniline, phenol, acetanilide, and Nitrophenol have activating groups making them more reactive than the rest of the compounds used. 2. Do your experimental results agree with the theoretical data? If not, what are the possible sources of error? No. The most probable source of error in this experiment would be human error. One example is how you observe the reaction. In this experiment where you are to perform reaction in dark, it is difficult to judge whether the reaction has already proceeded or not. It depends on the judgment of the experimenter when determining the reaction rates of certain compounds. Contamination or impurities in the compounds used might also be considered as one of the possible sources of error. 3. Predict the reactivity of the following compounds towards chlorination form the least reactive to the most reactive: A. Toluene, nitrobenzene, anisole, and methylbenzoate Nitrobenzene < methylbenzoate < toluene < anisole B. Benzene, acetophenone, bromobenzene, and benzyl alcohol Benzyl alcohol < acetophenone < bromobenzene < benzene C. Styrene, acetophenone, aniline, and iodobenzene Benzaldehyde < iodobenzene < styrene < aniline 4. Explain the effect of solvent in the reaction of acetanilide and Br2 in Part B.

In this part of the experiment, the effect of solvent in the reaction of acetanilide in reaction rate is determined. Based on the results, it can be concluded that the more polar the solvent used in this experiment, the faster the reaction would proceed. It took minutes for the reaction to complete when the solvent used is cyclohexane, which is a very non-polar solvent. While on the other hand, when the solvent used was acetic acid, which is a polar solvent, it just took one second for the reaction to complete. This is because acetic acid polarizes Br2 making Brmore electrophilic. In this way, the bromide ions can attack the nucleophilic benzene ring more easily. REFERENCES [1] McMurry, J. (2008). Organic chemistry. Pacific Grove, CA: Brooks/Cole Pub. [2] Retrieved from http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch12substituenteffects.html [3] Solomons, T. W., & Fryhle, C. B. (2011). Organic chemistry. Hoboken, NJ: Wiley.