Chem 226 / Dr. Rusay

Fall 1997

Your sense of smell can be highly senstitive to organic molecules. The nose serves as a chemical detector much like an analytical instrument. The vials that you are going to smell contain very dilute solutions of a single volatile compound. Your group will categorize several compounds according to their odor. The smell categories are: Fruity, Putrid, Minty, Camphoraceous or Other. You have only 30 minutes to develop your data once you have been advised to start so budget your time! Another 5 minutes will be alotted to orally present the results to the class. After each group reports their data, we will evaluate the results and then examine whether molecular formula relates to odor.

Directions

Sit with your assigned groups.

Each individual in the group must serve in one of the following roles. Quickly select your roles.

a) Sample manager: obtain sample vials, distribute vials one at a time to the group and keep track of the samples, return the vials after the activity is completed. Keep track of time and keep the group informed of how much time remains to complete the assignment.

b) Recorder #1: Have each member of your group classify each vial into one of the five categories and record the result. Also, write down a one-word description from each group member in their own language (use one of the following tables) for each sample.

c) Recorder #2: Write down any problems the group is having in describing the vials and/or in agreeing, e.g., an individual could not detect an odor, two people have colds, etc. (use one of the following tables).

d) Presenter: Facilitate group discussion as to which smells are similar and belong in the same category. Prepare a written summary of your categorizations to turn in with all of the group's names included (use one of the following tables) and make an oral report on behalf of the group to the entire class.

e) Group Responsibility: To complete the data on time and be prepared to present the results.

Group Names (Include name of each member participating) :

             Fruity          Putrid         Minty      Camphoraceous   Other

Comments:

Smell: Instructor's Notes and Guide

Please prepare 12 sets of sample vials for students to smell. 6 per section per instructor. Can re-use in later sections.The vials should seal well since the compunds are volatile.

1 set of six is for secs. 001/002 (Long)

1 set of six is for secs. 003/004 (Rusay)

Please label as noted: O-1 thru O-8 will be the same in both sets. It is important since empirical problems have already been written for these codes.

O-9 will be different for Long and Rusay.

Only Rusay will have O-10 and O-11.

Prepare sample soultions by diluting in ethanol 1 g or 1 ml of sample / 10 ml ethanol; 1,4-diaminopentane can be diluted 1:25 to 1:50 since it is very strong smelling.

Add a few mls of sample solution to a vial with a cotton ball. Seal and label O-1, O-2, etc.

The caraway seed can be added as grounds with the ethanol.

General Information and Background

• Anosmia, odor blindness, is like color blindness. 1.2% of all humans do not have a sense of smell. (Total anosmia). There are other types: 3% of population cannot distinguish between ethyl butyrate and caproic acid. 10% cannot distinguish between d- and l- carvone. Some people cannot smell banana (isoamyl acetate), others clove (eugenol). About 100 compounds are known to be undetectable by a restricted number of the population. There also are a relatively small number of individuals with hyperosmias, a condition of super sensitivity to odorants.

• Smell: effects diet, emotions and memory.

• Marcel Proust: "Helps us in the search for the past."

• Taste relates to: "sweet, sour, salty and bitter." Not limited by MW or polarity.

• Smell can distinguish between an almost infinite number of volatile compounds (highest know MW is 294, a labdane derivative) and at very low concentrations.

manool

One of the strongest odors comes from (+)-(R)-1-p-menthen-8-thiol which occurs in grapefruit juice and is detectable at 0.000021 ppb. Another strong odor is produced by 2,2-furfuryl thiol which is reported to be detectable at 0.005 ppb and said to smell like feshly brewed coffee at concentrations about an order of magnitude higher than the detection limit. Butter has 5-(Z)-Octa-1,5-dien-3-one (0.001 ppb), pepperoni has 2-methoxy-3-isobutylpyrazine (0.002 ppb) and strawberry has 2,5-dimethyl-4hydroxy-3(2H)-furanone (0.04 ppb).

• A steroidal ketone, 5-alpha-androst-16-en-3-one, a boar pheromone with a urine like odor, is detectable at relatively low concentrations (0.2 ppb); 70.5% of females and 62.8% of males out of 26,000 subjects could detect it). The process involves a stimulus and a receptor, a bi-molecular interaction. Emil Fischer and others referred to it as a "lock and key".

• A study by A.N. Gilbert and C.J. Wysocki, Nat. Geog. 19:514 (1987), of 1.5 million people who were asked if they could perceive 6 odors: 5-alpha-androst-16-en-3-one, isoamyl acetate, Galaxolide, eugenol, a mixture of mercaptans and rose perfume produced the following results:
• Females have greater sensiviy than males at all ages.
• Highest sensitivity is reached after puberty in both genders.
• Sensitivity decreases considerably by age 70 and drastically by 80.
• Hormonal body state relates to sensitivity.
• 1.2% of all humans do not have a sense of smell. (Total anosmia)
• In the study 62.4% indicated a temporary loss due to flu, cold or sinus infection.
• Smokers are bi-polarized. They are less sensitive to the steroid, eugenol and mercaptans but more sensitive to musks (Galaxolide) and isoamyl acetate (banana).
• Anosmias are pronounced in musks, amber odorants and compunds in sweat and urine.

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There are stereochemical differences between enantiomers. eg. d-carvone: spearmint and l-carvone: caraway. See complete list from: Gunther Ohloff, Scent and Fragrances, pp. 43-44, Springer-Verlag, 1994.

© Copyright 1997 R.J. Rusay