Organic Chemistry- Spectroscopy Flashcards Preview

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Flashcards in Organic Chemistry- Spectroscopy Deck (100)
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1

What procedure would be the most efficient to identify an unknown compound?

Spectroscopy

2

What is spectroscopy?

Measures the energy difference between the possible states of a molecular system by determining the frequencies of electromagnetic radiation absorbed by the molecules.

3

The different levels of the frequencies absorbered by the molecule are associated with different types of molecular motion like what?

Molecular rotation, vibration of bonds, electron absorption and nuclear spin

4

Different types of spectroscopy measure different types of _________?

Molecular properties.

5

Spectroscopty allows us to identify _______ and _______.

The presence of specific funtional groups and
The onnectivity (backbone) of a molecule.

6

In medical context, what is spectroscopy important in?

Magnetic resonance imaging (MRI)

7

MRI scanners actually measure what and then do what?

H-NMR spectra of water molecules in different environments in the body. They then convert these signals into greyscale, allowing excellent visualization of the body, especially soft tissue.

8

What is the big advantage of laboratory spectroscopy?

Only a small quantity of a sample is needed. Also the sample may be reused after a test is performed.

9

What is the downside of spectroscopy?

It's difficult to do without special equipment.

10

What does infrared spectroscopy measure?

Molecular vibrations, which can be seen as bond stretching, bending, or combinations of different vibrational modes.

11

How do you record the Infrared spectrum?

Infrared light is passed through a sample, and the absorbance is measured.

12

By determining the bonds in a molecule, what can be understood?

Hope to infer the functional groups in the molecule.

13

What is the infrared light range?

Wavelength of 700nm to 1mm

14

What is the useful absorptions for spectroscopy?

Wavelengths of 2500 to 25,000nm

15

On IR spectrum, we use an analog of frequency called what?

Wavenumber

16

What is the standard range of wavenumber?

2500 to 25,000nm is 4000 to 400cm^-1

17

When light of the standard range of wavnumber is reached what happens?

The molecules eneter excited vibrational states.

18

What are the types of vibrations that can occur in IR spectroscopy?

Twisting and folding

19

In Infrared spectroscopy, more complex vibration pattern are caused by what?

The motion of the molecule as a whole.

20

In IR spectroscopy, in what range can more complex vibration patterns be seen? What is it called?

1500 to 400cm^-1
Called the Fingerprint region

21

Why is it called the fingerprint region in IR spectroscopy?

The specific absorbance pattern is characteristic of each individual molecule

22

For an absorption to be recorded, the vibration must result in a change in what?

The bond dipole moment.

23

Which type of molecules do not exhibit absorption?

Molecules that do not experience a change in dipole moment, such as those composed of atoms with the same electronegativity or molcules that are symmetrical.

24

What are examples of molecules that do not exhibit absorption?

O2
Br2
Triple bond in acetylene (C2H2)

25

What groups do you need to memorize the absorptions?

Hydroxyl group

26

What does the absorption of the O-H group look like?

Absorbs with a broad (wide) peak at around one of two frequencies: 3300cm^-1 for alcohols, and 3000cm^-1 for carboxylic acids.

27

Why is the frequency for O-H group absorption lower for carboxylic acids?

The carbonyl of a carboxylic acid pulls some of the electron density out of the O-H bond, whifting the absorption to a lower wavelength.

28

What does the absorption for the carbonyl look like?

It absorbs around 1700cm^-1 with a sharp deep peak.

29

What are some common characteristics of absorption?

The bond between any atom and hydrogen always has a relatively high absorption frequency and how as we add more bonds between carbon atoms, the absorption frequency increases.

30

What does the N-H bonds absorption frequency look like?

It's in the same region as O-H bonds around (33oocm^-1) but have a sharp peak intead of a broad one.