有机化学英文课件chapter12
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12-3
Electromagnetic Radiation
Common units used to express wavelength
M acintosh P IC T im age form at
is not supported
M a c in to s h P IC T im a g e fo rm a t
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted
12-14
Hydrocarbons-Table 12.5
M acintosh PICT im age form at
is not supported
12-15
Alkanes
IR spectrum of decane (Fig 12.4)
12-26
Carbonyl groups
The position of C=O stretching vibration is
sensitive to its molecular environment
• as ring size decreases and angle strain increases, absorption shifts to a higher frequency
is n o t s u p p o rte d
12-24
IR of Molecules with C=O Groups
M acintosh P IC T im age form at
is not supported
12-25
Aldehydes and Ketones
IR spectrum of menthone (Fig 12.12)
Organic Chemistry
William H. Brown Christopher S. Foote Brent L. Iverson
12-1
Infrared Spectroscopy
Chapter 12
12-2
Electromagnetic Radiation
Electromagnetic radiation: light and other forms of radiant energy Wavelength (): the distance between consecutive peaks on a wave Frequency (): the number of full cycles of a wave that pass a given point in a second Hertz (Hz): the unit in which radiation frequency is reported; s-1 (read “per second”)
is n o t s u p p o rte d
12-4
Molecular Spectroscopy
Molecular spectroscopy: the study of which frequencies of electromagnetic radiation are absorbed or emitted by a particular substance and the correlation of these frequencies with details of molecular structure
Alcohols
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
• IR spectrum of 1-hexanol (Fig 12.8)
12-20
Ethers
IR spectrum of dibutyl ether (Fig 12.9)
H3 C CH3
CC
H3 C- C C- CH3
H3 C CH3
2,3-Dimethyl-2-butene 2-Butyne 12-9
Molecular Vibrations
For a nonlinear molecule containing n atoms, there are 3n - 6 allowed fundamental vibrations For even a relatively small molecule, a large number of vibrational energy levels exist and patterns of IR absorption can be very complex The simplest vibrational motions are bending and stretching
connected by the bond The intensity of absorption depends primarily on the polarity of the vibrating bond
12-13
Correlation Tables
Table 12.4 Characteristic IR absorptions for the types of bonds and functional groups we deal with most often
10-2 m•cm -1 =
= 400 cm-1
2.5 x 10-5 m
12-6
Infrared Spectroscopy
IR spectrum of 3-methyl-2-butanone
12-7
Molecular Vibrations
• atoms joined by covalent bonds undergo continual vibrations relative to each other
12-8
Molecular Vibrations
For a molecule to absorb IR radiation
• the bond undergoing vibration must be polar and
• its vibration must cause a periodic change in the bond dipole moment
• the total energy is proportional to the frequency of vibration
• the frequency of a stretching vibration is given by an equation derived from Hooke’s law for a vibrating spring
Covalent bonds which do not meet these criteria are said to be IR inactive
• the C-C double and triple bonds of symmetrically substituted alkenes and alkynes, for example, are IR inactive because they are not polar bonds
• the frequency of IR radiation is commonly expressed
in wavenumbers
•
wavenumber : Macintosh PICT im age form at is not supported
the
number
of
waves
per
centimeter,
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
K = a force constant, which is a measure of the bonds’ strength; force constants for single, double, and triple bonds are approximately 5, 10, and 15 x 105 dynes/cm
• the energies associated with these vibrations are quantized; within a molecule, only specific vibrational energy levels are allowed
• the energies associated with transitions between vibrational energy levels correspond to frequencies in the infrared region, 4000 to 400 cm-1
12-10
Molecular vibrations
Fundamental stretching and bending vibrations for a methylene group
12-11
Molecular Vibrations
Consider two covalently bonded atoms as two vibrating masses connected by a spring
• we study three types of molecular spectroscopy
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
12-5
Infrared Spectroscopy
The vibrational IR extends from 2.5 x 10-6 m (2.5 m) to 2.5 x 10-5 m (25 m)
12-16
Alkenes
IR spectrum of cyclohexene (Fig 12.5)
12-17
Alkynes
IR spectrum of 1-octyne (Fig 12.6)
12-18
Aromatics
IR spectrum of toluene (Fig 12.7)
12-19
is n o t s u p p o rte d
From this equation, we see that the position of a stretching vibration
• is proportional to the strength of the vibrating bond • is inversely proportional the masses of the atoms
= reduced mass of the two atoms, (m1m2)/(m1 + m2),
where m is the mass of the atoms in grams
12-12
Molecular Vibrations
M a c in to s h P IC T im a g e fo rm a t
with units cm-1 (read in wavenumbers, the vibrational IR extends from 4000 cm-1 to 400 cm -1
= 10-2 m•cm -1 = 4000 cm-1 2.5 x 10-6 m
O
O
O
O
1715 cm-1
1745 cm-1
1780 cm-1
1850 cm-1
• conjugation shifts the C=O absorption to lower
frequency
O
O O
H
1717 cm-1
12-21
Ethers
IR spectrum of anisole (Fig 12.10)
12-22
Amines
IR spectrum of 1-butanamine (Fig 12.11)
12-23
IR of Molecules with C=O Groups
M a c in to s h P IC T im a g e fo rm a t
Electromagnetic Radiation
Common units used to express wavelength
M acintosh P IC T im age form at
is not supported
M a c in to s h P IC T im a g e fo rm a t
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted
12-14
Hydrocarbons-Table 12.5
M acintosh PICT im age form at
is not supported
12-15
Alkanes
IR spectrum of decane (Fig 12.4)
12-26
Carbonyl groups
The position of C=O stretching vibration is
sensitive to its molecular environment
• as ring size decreases and angle strain increases, absorption shifts to a higher frequency
is n o t s u p p o rte d
12-24
IR of Molecules with C=O Groups
M acintosh P IC T im age form at
is not supported
12-25
Aldehydes and Ketones
IR spectrum of menthone (Fig 12.12)
Organic Chemistry
William H. Brown Christopher S. Foote Brent L. Iverson
12-1
Infrared Spectroscopy
Chapter 12
12-2
Electromagnetic Radiation
Electromagnetic radiation: light and other forms of radiant energy Wavelength (): the distance between consecutive peaks on a wave Frequency (): the number of full cycles of a wave that pass a given point in a second Hertz (Hz): the unit in which radiation frequency is reported; s-1 (read “per second”)
is n o t s u p p o rte d
12-4
Molecular Spectroscopy
Molecular spectroscopy: the study of which frequencies of electromagnetic radiation are absorbed or emitted by a particular substance and the correlation of these frequencies with details of molecular structure
Alcohols
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
• IR spectrum of 1-hexanol (Fig 12.8)
12-20
Ethers
IR spectrum of dibutyl ether (Fig 12.9)
H3 C CH3
CC
H3 C- C C- CH3
H3 C CH3
2,3-Dimethyl-2-butene 2-Butyne 12-9
Molecular Vibrations
For a nonlinear molecule containing n atoms, there are 3n - 6 allowed fundamental vibrations For even a relatively small molecule, a large number of vibrational energy levels exist and patterns of IR absorption can be very complex The simplest vibrational motions are bending and stretching
connected by the bond The intensity of absorption depends primarily on the polarity of the vibrating bond
12-13
Correlation Tables
Table 12.4 Characteristic IR absorptions for the types of bonds and functional groups we deal with most often
10-2 m•cm -1 =
= 400 cm-1
2.5 x 10-5 m
12-6
Infrared Spectroscopy
IR spectrum of 3-methyl-2-butanone
12-7
Molecular Vibrations
• atoms joined by covalent bonds undergo continual vibrations relative to each other
12-8
Molecular Vibrations
For a molecule to absorb IR radiation
• the bond undergoing vibration must be polar and
• its vibration must cause a periodic change in the bond dipole moment
• the total energy is proportional to the frequency of vibration
• the frequency of a stretching vibration is given by an equation derived from Hooke’s law for a vibrating spring
Covalent bonds which do not meet these criteria are said to be IR inactive
• the C-C double and triple bonds of symmetrically substituted alkenes and alkynes, for example, are IR inactive because they are not polar bonds
• the frequency of IR radiation is commonly expressed
in wavenumbers
•
wavenumber : Macintosh PICT im age form at is not supported
the
number
of
waves
per
centimeter,
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
K = a force constant, which is a measure of the bonds’ strength; force constants for single, double, and triple bonds are approximately 5, 10, and 15 x 105 dynes/cm
• the energies associated with these vibrations are quantized; within a molecule, only specific vibrational energy levels are allowed
• the energies associated with transitions between vibrational energy levels correspond to frequencies in the infrared region, 4000 to 400 cm-1
12-10
Molecular vibrations
Fundamental stretching and bending vibrations for a methylene group
12-11
Molecular Vibrations
Consider two covalently bonded atoms as two vibrating masses connected by a spring
• we study three types of molecular spectroscopy
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
12-5
Infrared Spectroscopy
The vibrational IR extends from 2.5 x 10-6 m (2.5 m) to 2.5 x 10-5 m (25 m)
12-16
Alkenes
IR spectrum of cyclohexene (Fig 12.5)
12-17
Alkynes
IR spectrum of 1-octyne (Fig 12.6)
12-18
Aromatics
IR spectrum of toluene (Fig 12.7)
12-19
is n o t s u p p o rte d
From this equation, we see that the position of a stretching vibration
• is proportional to the strength of the vibrating bond • is inversely proportional the masses of the atoms
= reduced mass of the two atoms, (m1m2)/(m1 + m2),
where m is the mass of the atoms in grams
12-12
Molecular Vibrations
M a c in to s h P IC T im a g e fo rm a t
with units cm-1 (read in wavenumbers, the vibrational IR extends from 4000 cm-1 to 400 cm -1
= 10-2 m•cm -1 = 4000 cm-1 2.5 x 10-6 m
O
O
O
O
1715 cm-1
1745 cm-1
1780 cm-1
1850 cm-1
• conjugation shifts the C=O absorption to lower
frequency
O
O O
H
1717 cm-1
12-21
Ethers
IR spectrum of anisole (Fig 12.10)
12-22
Amines
IR spectrum of 1-butanamine (Fig 12.11)
12-23
IR of Molecules with C=O Groups
M a c in to s h P IC T im a g e fo rm a t