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Organic Chemistry > IR Spectroscopy > Flashcards

IR Spectroscopy Flashcards

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1
Q

What information can we get from IR spectroscopy?

A

Information about functional groups

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2
Q

What does the x axis of an IR spectrum give us information about?

A

The frequency of light absorbed (bond strength).

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3
Q

What does the y axis give us information about?

A

How much light is absorbed (the dipole of the functional group).

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4
Q

In what area of an IR spectrum will you see signals for H-C (sp3) bonds?

A

2850 - 3000 cm^-1

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5
Q

If you have stretches between 2850 and 3000 cm^-1, what functional group do you have?

A

H-C (sp3) bonds

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6
Q

In what area of an IR spectrum will you see signals for H-C (sp2) bonds?

A

3000 - 3100 cm^-1

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7
Q

If you have stretches between 3000 and 3100 cm^-1, what functional group do you have?

A

H-C (sp2) bonds

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8
Q

How does greater s character in a hybrid orbital affect a stretch in an IR spectrum?

A

Greater s character will result in a shorter, stronger bond and, therefore, a higher absorption.

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9
Q

If you have a sharp stretch at 3300 cm^-1, what functional group do you have?

A

H-C (sp)

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10
Q

In what area of an IR spectrum will you see signals for H-C (sp) bonds?

A

Sharp stretch at 3300 cm^-1

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11
Q

What functional group do you have if you have a strong, broad stretch from 3200 - 3600 cm^-1?

A

An alcohol

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12
Q

In what area of an IR spectrum will you see the stretch for an alcohol O-H bond?

A

3200-3600 cm^-1

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13
Q

In what area of an IR spectrum will you see the stretch for an carboxylic acid O-H bond?

A

2200 - 3600 cm^-1

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14
Q

In what areas of an IR spectrum will you see the stretches for a carboxylic acid functional group?

A

1) Broad stretch between 2200 and 3600 cm^-1

2) Sharp stretch between 1700 and 1750 cm^-1

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15
Q

In what area of an IR spectrum will you see the stretch for an carboxylic acid O-C double bond?

A

1700-1750 cm^-1

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16
Q

What functional group do you have if you have a single, moderate stretch between 3350 and 3500 cm^-1?

A

A secondary amine

17
Q

What functional group do you have if you have two moderate stretches between 3350 and 3500 cm^-1?

A

A primary amine

18
Q

What sort of signal will a primary amine produce?

A

Two moderate stretches between 3350 and 3500 cm^-1

19
Q

What sort of signal will a secondary amine produce?

A

One moderate stretch between 3350 and 3500 cm^-1

20
Q

What sort of signal will an aldehyde C-H bond produce?

A

2750-2850 cm^-1, but hard to see

21
Q

How will an EDG adjacent to a carbonyl affect the carbonyl’s signal in IR spectroscopy? Why?

A

The carbonyl stretch will be observed at a lower frequency, because the EDG stabilizes the charge-separated resonance contributor, giving the group more single-bond character.

22
Q

How will an EWG adjacent to a carbonyl affect the carbonyl’s signal in IR spectroscopy? Why?

A

The carbonyl stretch will be observed at a higher frequency, because the EWG destabilizes the charge-separated resonance contributor, giving the group less single-bond character.

23
Q

Where will the stretch for a C-C triple bond be on an IR spectrum?

A

2100-2200 cm^-1

24
Q

Where will the stretch for a C-N triple bond be on an IR specturm?

A

2200-2300 cm^-1

25
Q

Where will an acid halide carbonyl bond be found on an IR spectrum?

A

1750-1850 cm^-1

26
Q

What functional group do you have if you see a sharp stretch between 2200 and 2300 cm^-1 on an IR spectrum?

A

A C-N triple bond

27
Q

What functional group do you have if you see a sharp stretch between 2100 and 2200 cm^-1 on an IR spectrum?

A

A C-C triple bond

28
Q

Where do esters stretches occur?

A

1740 cm^-1

29
Q

What sort of carbonyl stretch occurs at about 1740 cm^-1?

A

An ester

30
Q

What sorts of carbonyl stretches occur at about 1710 cm^-1?

A

Ketones

31
Q

Where do amide carbonyl stretches usually occur?

A

1650 cm^-1

32
Q

What sorts of carbonyl stretches occur at about 1725 cm^-1?

A

Aldehydes

33
Q

How can you tell if a stretch around 1710 cm^-1 is a ketone or an aldehyde?

A

An aldehyde will have another stretch (hard to see) between 2700 and 2800 cm^-1.

34
Q

How does conjugation affect a group’s signal in IR spectroscopy? Why?

A

It lowers it, because it gives the bond more single-bond character.

35
Q

In what range of the IR spectrum do we find the stretches for C-C double bonds?

A

At about 1600 cm^-1

36
Q

Where will we find a benzene stretch?

A

1480 cm^-1

37
Q

Where will we find a cyclohexene stretch?

A

1650 cm^-1

Organic Chemistry (7 decks)

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