Assessment 3

Question 1

Absorption (infrared) spectroscopy

Answer 1

Involves passing a beam of electromagnetic radiation through a sample. Some radiation is absorbed (attenuated) by the sample, and the rest is transmitted (passes through the sample). Absorbance/Transmittance is measured as a function frequency or wavelength.

Question 2

Relationship between frequency and wavelength

Answer 2

Waves like gamma rays and X-rays have a high frequency and a short wavelength, while microwaves and radio waves have a lower frequency and a longer wavelength

Question 3

Components of infrared spectroscopy

Answer 3

A sample is radiated with infrared light, and the light reacts with components in the sample, where some light is absorbed and some light passes through. It eventually reaches a detector, where it can tell us about the structure of the molecule

Question 4

Why do we use infrared light for spectroscopy?

Answer 4

At baseline, molecules exhibit translational motion, as heat energy is converted to kinetic energy even in solids. Bonds are constantly rotating, so rotational motion occurs as well. However, a specific wavelength of infrared radiation can induce new behaviors (vibrational motion) in the chemical bonds, causing them to stretch or twist. These types of vibrational motions occur at specific light energies, and the response of the molecule varies depending on its functional group. This is how we can use IR to determine the functional groups of a molecule

Question 5

x axis of IR spectra

Answer 5

Wave number- tells us about the particular energy of infrared light

Question 6

y axis of IR spectra

Answer 6

% transmittance- percentage of that specific wave number that reaches the detector. 100% transmittance would mean that all of the light moved through the sample without being absorbed at all.

Question 7

When atoms vibrate when they are radiated, which factors determine the frequency?

Answer 7

Mass of atoms and bond stiffness/strength. Lighter atoms and stronger bonds have a higher vibrational frequency

Question 8

Radiant energy absorbed causes transitions from

Answer 8

v-ground-state to v-excited state. IR absorption is accompanied with change in dipole moment during vibration

Question 9

The intensity of IR bands depends on

Answer 9

The magnitude of the dipole moment associated with the bond interacting with IR radiation

Question 10

What makes a molecule IR active/inactive?

Answer 10

A molecule will be inactive if it doesn’t have a change in dipole moment after it’s exposed to IR radiation

Question 11

Functional group region of IR

Answer 11

The high energy region with a wavenumber greater than 1200 cm. It is associated with specific bond types and is used to identify the presence/absence of a functional group

Question 12

Fingerprint region of IR

Answer 12

The lower energy region with a wavenumber less than 1200 cm. It is composed of absorptions that are characteristic of a compound

Question 13

IR band classifications based on relative intensity

Answer 13

Can be strong, medium, or weak depending on peak high. Strong peaks cover 75% of the y axis or more, while weak peaks cover 20% or less

Question 14

IR band classifications based on peak shape

Answer 14

Can be broad band or narrow (sharp) band

Question 15

Purpose of Diels-Alder experiment

Answer 15

The purpose of the experiment was to use an unknown diene in a sample of eucalyptus oil and maleic anhydride to form a Diels-Alder adduct.

Question 16

Diels-Alder reaction

Answer 16

The Diels-Alder reaction is a reaction between a diene that contains two conjugated pi bonds and a dienophile that contains one or more pi bonds, which ultimately forms a six carbon ring. During the reaction, two new single bonds are formed between the diene and the dienophile, and one new double bond is formed in the diene. The reaction occurs in one step and results in endo and exo products, with endo being the major product.

Question 17

Which methods were used to carry out a Diels-Alder reaction?

Answer 17

Reflux is a method used to heat the solution in order to increase the rate of the reaction. It involves boiling the solution in a closed system, so that none of the solvent is lost through evaporation. A solution containing the unknown diene, maleic anhydride, and anhydrous ethyl ether was heated in the reflux apparatus. The final product was allowed to crystallize and was isolated using vacuum filtration. Melting point was used to identify the unknown diene.

Question 18

How was the theoretical amount of product calculated for a Diels-Alder reaction?

Answer 18

In order to calculate the theoretical amount of the product, the area of the diene’s peak on a gas chromatogram was compared to the total surface area of the chromatogram in order to determine the percentage of the diene in the oil sample. The percentage was used to calculate the grams and moles of the diene, and these numbers were used to calculate the theoretical amount of product.

Question 19

What was the diene and what was the dienophile in the Diels-Alder reaction?

Answer 19

The diene was included in the essential oil sample. The dienophile was maleic anhydride

Question 20

Fischer esterification

Answer 20

The process of heating a carboxylic acid with an alcohol in order to form an ester as a product, using an acid as a product. The reaction begins with the carbonyl of the carboxylic acid being protonated by the acid, and the carboxylic acid then undergoes a nucleophilic attack by the alcohol. This step forms a tetrahedral intermediate compound, which is unstable. Dehydration and then deprotonation by the base occurs, resulting in an ester and water

Question 21

Purpose of Fischer esterification experiment

Answer 21

To use Fischer esterification in order to synthesize an unknown acetate ester, and to use organic spectroscopy in addition to the compound’s physical properties to identify the unknown compound. In this experiment, an unknown alcohol was reacted with ethanoic acid with sulfuric acid as a catalyst, and the reaction was carried out during the reflux process.

Question 22

How can reverse of Fischer esterification be prevented?

Answer 22

Fischer esterification is reversible, so the ester and water products could react to form the original carboxylic acid and alcohol through hydrolysis. According to Le Chatelier’s principle, this outcome can be prevented by using an excess of the starting reagent to shift equilibrium to the right side, which is the side of ester formation. Le Chatelier’s principle states that equilibrium is disrupted by changing the conditions of the reaction, the equilibrium will shift to adjust to the change . In this case, the acetate ester is added in excess, and the reaction compensates for an increase in the concentration of the reactants by creating more product.

Question 23

What techniques were used during Fischer esterification?

Answer 23

Reflux, extraction, and distillation. Sodium sulfate is used as a drying agent to remove water. Refractive index is one method used to identify the compound

Question 24

Why is reflux used in Fischer esterification?

Answer 24

Heating of the reactants is necessary in order for the reaction to occur, and reflux is done in order to heat the sample without any of the reactants being lost due to evaporation

Question 25

Why is extraction used in Fischer esterification?

Answer 25

Takes advantage of each compound’s differences in solubility and reactivity in order to remove sulfuric acid from the sample. The acid in the sample reacts with 10% sodium bicarbonate, and loses a proton to become ionic. Therefore, it will be soluble in the aqueous portion of the solution and be separated from the organic portion containing the ester.

Question 26

Why is distillation used in Fischer esterification?

Answer 26

Simple distillation was performed in order to separate the components of the mixture on the basis of their boiling points. The final ester product was isolated in the distillation fraction.

Question 27

Refractive index

Answer 27

A measure of how quickly a specific wavelength of light passes through a compound. Certain wavelengths interact with each compound differently, so each compound has a unique refractive index at a specific temperature. The refractive index was one method used to identify the ester in this experiment, along with NMR and IR spectroscopy.