Spectroscopy and Structure Determination Flashcards by Jhaunte Braithwaite

What is spectroscopy?

A technique used to determine the structure of a compound

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What in spectroscopy is often used to determine structure?

Material’s absorption or emission of energy in a defined portion of the electromagnetic spectrum

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What is absorption spectroscopy?

Spectroscopy that measures the amount of light absorbed by the sample as a function of wavelength.

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Most spectroscopy techniques are ______________

Nondestructive

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What is infrared spectroscopy?

Spectroscopy that measures the bond vibration frequencies in a molecule and is used to determine a functional group

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What is mass spectroscopy?

Spectroscopy that fragments the molecule and measures their mass.

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What information can be obtained using mass spectroscopy?

Mass spectroscopy can give the molecular weight of the compound and functional groups

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What is Nuclear Magnetic Resonance spectroscopy?

NNR spectroscopy analyzes the environment of the hydrogens in a compound which gives useful clues to alkyl and other functional groups present

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What is Ultraviolet Spectroscopy?

Spectroscopy that uses electronic transitions to determine bonding patterns

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Which of the following spectroscopy does NOT use absorption spectroscopy?

UV spectroscopy, NMR spectroscopy, MS spectroscopy, IR spectroscopy

Mass spectroscopy

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Why is electromagnetic radiation said to have dual behavior?

Behaves as a particle(photon) in some some respects and a wave in other respects

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Due to its wave like behavior, electromagnetic radiation can be characterized by….

A frequency

A wavelength

An amplitude

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What is the amplitude of the wave?

The height of the wave measured from midpoint to peak

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In electromagnetic radiation, intensity of radiant energy is proportional to…

To the square if the Wave’s amplitude

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What is the intensity of radiant energy of a feeble glow?

It is proportional to the square of the wave’s amplitude

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What is wavelength?

The distance between any 2 peaks or any two troughs of the wave

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What is the frequency of a wave?

The number of complete cycles that pass a fixed point in a second

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Define the speed of light in terms of electromagnetic radiation

The rate of travel of all electromagnetic radiation in a vacuum

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Frequency and wavelength are __________ ______

Inversely proportional

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What is the speed and of a wave(speed of light for electromagnetic waves)

C= frequency x wavelength

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What is the speed of light?

3x 10^10cm/sec

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What are the units of electromagnetic radiation?

Quanta

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What does planks equation represent?

The amount of energy corresponding to 1 quanta of energy or 1 photon of a given frequency

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Give 2 formulas for energy

Energy = plank’s constant x frequency

Energy= plank’s constant x c/ wavelength (c=speed of light)

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What is plank’s constant(h)?

6.62x10^-37kj sec

What is the wavelength of visible light?

10^-4cm

What is the energy of visible light?

10^2kj/mol

What is the wavelength off gamma rays?

10^-9cm

What is the energy of vacuum UV?

10^3

What is the wavelength of Infrared radiation?

10^-3

What is the wavelength of a microwave?

10^-1

What is the energy of infrared energy?

10 kJ/mol

What happens to organic compounds when exposed to electromagnetic radiation?

It absorbs energy of certain wavelengths but transmits energy of other wavelengths

What are the wavelengths if the infrared region?

2.5x10^-4 to 25x10^-4

Describe the region of IR region?

From right below the visible region to just above the highest microwave and radar frequencies

What are wavenumbers?

The reciprocals of Wavelength (cm^-1)

What is the primary use of IR spectroscopy and why?

To identify vibrational frequencies as it uses vibrations which may coincide with vibrational modes within a molecule like bind stretching and bond angle bending that occurs in all molecules that occur above temperatures above absolute zero.

What is the wavelength of of X rays?

10 ^-7 cm or 700nm to 1mm

What are the molecular effects of X rays?

Ionization

What is the molecular effect of near UV radiation?

Electronic transitions

What are the molecular effects of infrared radiation?

Molecular vibrations

What are molecular effects of microwaves?

Rotational spin

What are the molecular effects of radio waves?

Nuclear spin transitions?

What is infrared spectroscopy?

The absorption of energy in the infrared region of the electromagnetic spectrum

How does infrared spectroscopy work?

Energy in the infrared region coincides with vibrational modes within a molecule such as the bond stretching and the bong angle bending that occurs in all molecules at temperatures above absolute zero

Why is IR spectroscopy used to identify functional groups?

IR spectroscopy vibrational frequencies are highly indicative of functional groups

Why does an organic molecule absorb some wavelengths of IIR radiation but not others

All molecules have a certain amount of energy and are in constant motion. Their bond stretch and contract, their atoms-wag back and forth and other vibrational molecules occur. The molecule an only stretch or bend only at specific frequencies corresponding to specific energy levels

How can IR spectroscopy be used to increase spring action in molecules to identify functional groups?

When the molecule is irradiated with electromagnetic radiation, energy is absorbed if the frequency of the of the radiation matches the frequency of molecule vibration Energy absorption causes an increased vibration the spring connecting the 2 atoms stretches and compresses a bit further

What are the ONLY 2 molecules that will give the same IR spectrum ?

Enantiomers

What region is the fingerprint region?

600-1400 cm ^-1 and has the most complex vibrations

What is the region for the most common vibrations?

1600-350.cm^-1

What is the C=O absorption range in ketones?

1670-1750cm^-1

What is the absorption of O-H in alcohols absorption range?

3400-3650cm^-1

What is the absorption range of C=C in alkenes?

1640-1680 cm^-1

What is the absorption of C-H in alkanes?

2850-2960 cm ^-1

What is the absorption range of =C-H. bond in alkenes?

3020-3100 cm ^-1

What is the absorption range of triple bond,C-H in alkynes?

3300cm^-1

What is the absorption range in C triple bond C in alkynes?

2100-2260 cm^-1

Stronger bonds absorb _____________ frequencies because the bond is ___________ to stretch

Higher Difficult

What Frequency does C-C bonds absorb?

1200cm^-1 Carbon =6 so 2 carbons...12

Explain how conjugation affects frequency. Use the C=C

Conjugation lowers frequencies isolated C=C: 1640-1680cm^-1 Conjugated C=C:1620-1640cm^-1 Aromatic C=C: 1600cm^-1

How does an s character in hybrid orbitals affect C-H bonds?

A greater percent s character in the hybrid orbitals increases C-H bond

What is the s character percentage of sp3, sp2 and sp carbons?

Sp3 is 25%, Sp2 is 33% and Sp is 50%

Compare and contrast O-H and N-H stretching in IR spectroscopy

Both occur at around 3300cm^-1 O-H is broad with a rounded tip Secondary amine is R2NH broad with one sharp spike Primary amine RNH2 is broad with 2 sharp spike No signal for tertiary amine as it has no hydrogen

What causes the broad intense stretching of O-H?

Due to diverse nature of hydrogen bonding interactions of alcohol m9lecules

Describe and give reason for the spike in dipropylamine

Has a single hydrogen on N-H so it will have one spike

What is absorption (not range) C=O of simple. Ketones, aldehydes and carboxylic acids?

Around 1710cm^-1

Usually the _______________ is the strongest IR. signal

Carbonyl

Aldehydes have two C-H bonds with signals around _________ and ___________ cm^-1

2700 2800

What is the range of the hydroxyl group of a carboxyl group?

2500-3500 cm^-1

Amides show a strong absorption for C=O at ________ to _________ cm^-1

1630 1660

Describe nitriles in IR spectroscopy

Carbon nitrogen triple bond has an intense and sharp absorption at around 2200 -2300

Why do nitriles produce stronger absorption’s than alkanes?

Nitrile bonds are more polar than carbon-carbon triple bonds

What is the energy of gamma rays?

10^7 kJ/mol

What is the range of wavelengths for radio waves?

Remember these are building sized. So >10cm. His slides have 10^2 and 10^4

What is the wavelength of near UV?

10^-5

What is the energy of an X ray?

10^5 kJ/mol

What are the energies per mole of radio waves?

About 10^-2 to 10^-6

Differentiate the carbonyl group C=O in ketones, acids, aldehydes,ester and amides

Ketones and acids- 1710cm^-1 Aldehydes- 1725cm^-1 Esters- 1735cm^-1 Conjugation lowers frequency Amides- 1650cm^-1

What are the nitriles absorption? C triple bond N

2210-2260

Describe the absorption and intensity of C-O

1050-1150 with strong intensity

Describe the absorption and intensity of N-H bonds in amines amides

3300 cm^-1

What frequency is C-O in alcohol?

1050-1150

What bond has a frequency of 1050-1150?

C-O in alcohols

What is the O-H bond in alcohol?

3400-3650

What bond has a frequency of 3400-3650?

O-H in alcohols

What is the frequency of amines’ N-H?

3300-3500

What is the functional group that has a frequency of 3300-3500 with medium intensity?

N-H in amines

What is the frequency of C-N functional group in amines?

1030-1230

What functional group has a frequency of 1030-1230?

C-N in amines

What is the frequency of C-Cl?

600-80p

What functional group has the frequency 600-800?

C-Cl

What is the frequency of C-Br?

500-600

What functional group has the frequency 500-600?

C-Br

Wave numbers are proportional to ______ and ________

Frequency Energy

What is the frequency of an imine functional group?(C=N)

About 1660

Compare alkene to imine bonds

Imine (C=N) is stronger than alkene C=C