CHM138H1 Jasmyn Lee 1 Chapter 17: Alcohols and IR Spectroscopy
CHM138H1 Jasmyn Lee
Chapter 17: Alcohols and IR Spectroscopy 17.1 Naming Alcohols and Phenols Nomenclature
17.2 Properties of Alcohols and Phenols Structure
Physical Properties Interact by: 1) Dipole-Dipole Interactions 2) Hydrogen Bonding – allows for higher boiling point Constitutional Isomers
Acidity and Basicity of Alcohols In strong acids, alcohols can act as bases: o Reversibly protonated by strong acids to yield oxonium ions, ROH2+
In dilute aqueous solution, alcohols are weakly acidic: o Dissociate slightly by donating H+ to H2O, generating H3O+ and an alkoxide ion, RO- or a phenoxide ion, ArO-
o Ka = [RO-][H3O+] / [ROH] pKa = -logKa An alcohol is more acidic if its o Conjugate base has resonance and is therefore stabilized o If it has EWG (inductive effects) to delocalize the negative charge on the conjugate base Phenol Acidity
1
17.3 Preparations of Alcohols 1) (Indirect) Hydration of Alkenes a. Hydroboration – oxidation yields the product of syn, non-Markovnikov hydration
CHM138H1 Jasmyn Lee
b. Oxymercuration-demercuration – yields the product of Markovnikov hydration
2) Hydroxylation – OsO4 followed by a reduction with NaHSO3 17.4 Alcohols from Carbonyl Compounds: Reduction 3) Reduction of Carbonyl Functional Groups
o
NaBH4 – mild reducing agent (reduces only aldehydes and ketones)
o
LiAlH4 – stronger reducing agent – reduces all carbonyl compounds
a. Aldehydes and Ketones: NaBH4 in water or alcohols or LiAlH4 in ether Aldehydes 1° alcohols Ketones 2° alcohols
2
b. Esters and Carboxylic Acids: LiAlH4 in ether
CHM138H1 Jasmyn Lee
17.5 Alcohols from Carbonyl Compounds: Grignard Reactions 4) Reactions of Carbonyls with Grignard Reagents Recall: Grignard Reagents – prepared by reaction of organohalides with magnesium Grignard reagents react with carbonyl compounds to yield alcohols o Formaldehyde 1° alcohol o Aldehydes 2° alcohol o Ketones 3° alcohol Ester 3° alcohols in which two of the substituents bonded to the hydroxyl-bearing carbon have come from the Grignard reagent Carboxylic Acids hydrocarbon and the magnesium salt of the acid; does not yield an alcohol
17.6 Reactions of Alcohols 1) Deprotonation o Reaction with strong bases (pKa of conjugate acid > ~18)
o
Reaction with NaH (strong base)
o
Reaction with organolithium
3
2) Conversion of “-OH” into Better Leaving Groups Conversion of Alcohols into Alkyl Halides 3° Alcohols o SN1 Reaction o Acid protonates the hydroxyl oxygen atom, water is expelled to generate a carbocation o Cation reacts with nucleophilic halide ion to give the alkyl halide product
CHM138H1 Jasmyn Lee
1° and 2° alcohols o L=SOCl2 or PBr3 o Converts the –OH into a better leaving group o Inversion at the stereocenter
Conversion of Alcohols into Tosylates Alcohols react with p-toluenesulfunul chloride (tosyl chloride, p-TosCl) in pyridine solution to yield alkyl Tosylates, ROTos Only the O-H bond of the alcohol is broken in this reaction o C-O bond remains intact o SN1 and SN2 reactions Converts the –OH into a better leaving group Retention at the stereocenter
4
CHM138H1 Jasmyn Lee
3) Dehydration to Yield Alkenes: 3° Alcohols Acid catalyzed reaction of 3° Alcohols o o o
o o
Usually follow Zaitsev’s rule and yields the more stable alkene E1 process 3 step mechanism Protonation of the alcohol oxygen Unimolecular loss of water to generate a carbocation intermediate Final loss of a proton from neighboring carbon atom 3° alcohols react fastest because they lead to stabilized, tertiary carbocation intermediates 2° alcohols can be made to react, but conditions are severe and sensitive molecules do not survive
17.7 Oxidation of Alcohols 4) Oxidation of Alcohols Alcohol to carbonyl compound o 1° alcohols aldehydes
o
2° alcohols ketones
o
3° alcohols don’t react
Cr(VI) oxidation in acidic conditions oxidizes aldehydes to carboxylic acids
5
CHM138H1 Jasmyn Lee Usually compounds of Cr (VI) or Mn(VII) o KMnO4, CrO3, Na2Cr2O7 Cr(VI) as Oxidizing Agent o Typically carried out in acidic aqueous solvents in which the oxidant is HCrO4- and/or Cr2O72o 1° alcohols aldehyde (intermediate) carboxylic acids
KMnO4 as oxidizing agent o Typically carried out in acidic or basic aqueous solvents
PCC: Pyridium Chlorochromate
Breathalyzers and Intoxilizers – used to detect CH3CH2OH on breath o The breathalyzer device contains: Two glass vials containing the chemical reaction mixture A system of photocells connected to a meter to measure the color change associated with the chemical reaction
Dess Martin Periodinane – another mild oxidant in dichloromethane solvent o 1° alcohol to aldehyde
6
CHM138H1 Jasmyn Lee
o 2° alcohol to ketone 1. Substitution reaction between the alcohol and the I(V) reagent to form a new periodinane intermediate 2. Expulsion of reduced I(III) as the leaving group
17.11 Spectroscopy of Alcohols and Phenols 12. 5 Spectroscopy and the Electromagnetic Spectrum Electromagnetic Spectrum: o Gamma rays, X rays, ultraviolet, visible, infrared, microwaves, radio waves 12.6 Infrared Spectroscopy Infrared (IR) Spectroscopy E = hν = hc (1/λ) Wavenumber – the number of waves per centimeter = cm-1; reciprocal of wavelength
Infrared radiation causes excited vibrations in molecules: o Stretching: Symmetric Asymmetric
o
o o o
Bending: In-plane
Out-of-plane
Stretching energies > bending energies Roughly 1015 vibrations/sec A molecule can stretch and bend only at a specific frequency, corresponding to specific energy levels When a molecule is irradiated with electromagnetic radiation, energy is absorbed if the frequency of the radiation matches the frequency of the vibration Causes increased amplitude for the vibration
7
CHM138H1 Jasmyn Lee
12.7 Interpreting Infrared Spectra Different functional groups vibrate at different energies, allowing identification of functional groups in a molecule The energies of many functional group vibrations are largely independent of the structure of the rest of the molecule Fingerprint Region – 1500 cm-1 – 400 cm-1
–O-H 3200 to 3600 cm-1 –C=O 1680 to 1800 cm-1 (strong, sharp) If there is a strong peak at 180 to 1800 cm-1, the molecule has a C=O group
8
CHM138H1 Jasmyn Lee If there is NO peak at 1680 to 1800 cm-1, the molecule DOES NOT have a C=O group If there is a peak at 3200 to 3600 cm-1, the molecule has an –O-H group If there is NO peak at 3200 to 2600 cm-1, the molecule DOES NOT have an –O-H group
Intoxilyzer 5000EN: AlcoBlow Following in the tradition of the intoxilyzer 4011 and the intoxilyzer 5000, the intoxilyzer 5000EN enhances the court-tested reliability and accuracy of evidential infrared spectrometry breath alcohol testing The intoxilyzer 5000EN is backed by CMI’s factory service and support The Intoxilyzer device uses IR spectroscopy:
9
Chapter 17: Alcohols and IR Spectroscopy 17.1 Naming Alcohols and Phenols Nomenclature
17.2 Properties of Alcohols and Phenols Structure
Physical Properties Interact by: 1) Dipole-Dipole Interactions 2) Hydrogen Bonding – allows for higher boiling point Constitutional Isomers
Acidity and Basicity of Alcohols In strong acids, alcohols can act as bases: o Reversibly protonated by strong acids to yield oxonium ions, ROH2+
In dilute aqueous solution, alcohols are weakly acidic: o Dissociate slightly by donating H+ to H2O, generating H3O+ and an alkoxide ion, RO- or a phenoxide ion, ArO-
o Ka = [RO-][H3O+] / [ROH] pKa = -logKa An alcohol is more acidic if its o Conjugate base has resonance and is therefore stabilized o If it has EWG (inductive effects) to delocalize the negative charge on the conjugate base Phenol Acidity
1
17.3 Preparations of Alcohols 1) (Indirect) Hydration of Alkenes a. Hydroboration – oxidation yields the product of syn, non-Markovnikov hydration
CHM138H1 Jasmyn Lee
b. Oxymercuration-demercuration – yields the product of Markovnikov hydration
2) Hydroxylation – OsO4 followed by a reduction with NaHSO3 17.4 Alcohols from Carbonyl Compounds: Reduction 3) Reduction of Carbonyl Functional Groups
o
NaBH4 – mild reducing agent (reduces only aldehydes and ketones)
o
LiAlH4 – stronger reducing agent – reduces all carbonyl compounds
a. Aldehydes and Ketones: NaBH4 in water or alcohols or LiAlH4 in ether Aldehydes 1° alcohols Ketones 2° alcohols
2
b. Esters and Carboxylic Acids: LiAlH4 in ether
CHM138H1 Jasmyn Lee
17.5 Alcohols from Carbonyl Compounds: Grignard Reactions 4) Reactions of Carbonyls with Grignard Reagents Recall: Grignard Reagents – prepared by reaction of organohalides with magnesium Grignard reagents react with carbonyl compounds to yield alcohols o Formaldehyde 1° alcohol o Aldehydes 2° alcohol o Ketones 3° alcohol Ester 3° alcohols in which two of the substituents bonded to the hydroxyl-bearing carbon have come from the Grignard reagent Carboxylic Acids hydrocarbon and the magnesium salt of the acid; does not yield an alcohol
17.6 Reactions of Alcohols 1) Deprotonation o Reaction with strong bases (pKa of conjugate acid > ~18)
o
Reaction with NaH (strong base)
o
Reaction with organolithium
3
2) Conversion of “-OH” into Better Leaving Groups Conversion of Alcohols into Alkyl Halides 3° Alcohols o SN1 Reaction o Acid protonates the hydroxyl oxygen atom, water is expelled to generate a carbocation o Cation reacts with nucleophilic halide ion to give the alkyl halide product
CHM138H1 Jasmyn Lee
1° and 2° alcohols o L=SOCl2 or PBr3 o Converts the –OH into a better leaving group o Inversion at the stereocenter
Conversion of Alcohols into Tosylates Alcohols react with p-toluenesulfunul chloride (tosyl chloride, p-TosCl) in pyridine solution to yield alkyl Tosylates, ROTos Only the O-H bond of the alcohol is broken in this reaction o C-O bond remains intact o SN1 and SN2 reactions Converts the –OH into a better leaving group Retention at the stereocenter
4
CHM138H1 Jasmyn Lee
3) Dehydration to Yield Alkenes: 3° Alcohols Acid catalyzed reaction of 3° Alcohols o o o
o o
Usually follow Zaitsev’s rule and yields the more stable alkene E1 process 3 step mechanism Protonation of the alcohol oxygen Unimolecular loss of water to generate a carbocation intermediate Final loss of a proton from neighboring carbon atom 3° alcohols react fastest because they lead to stabilized, tertiary carbocation intermediates 2° alcohols can be made to react, but conditions are severe and sensitive molecules do not survive
17.7 Oxidation of Alcohols 4) Oxidation of Alcohols Alcohol to carbonyl compound o 1° alcohols aldehydes
o
2° alcohols ketones
o
3° alcohols don’t react
Cr(VI) oxidation in acidic conditions oxidizes aldehydes to carboxylic acids
5
CHM138H1 Jasmyn Lee Usually compounds of Cr (VI) or Mn(VII) o KMnO4, CrO3, Na2Cr2O7 Cr(VI) as Oxidizing Agent o Typically carried out in acidic aqueous solvents in which the oxidant is HCrO4- and/or Cr2O72o 1° alcohols aldehyde (intermediate) carboxylic acids
KMnO4 as oxidizing agent o Typically carried out in acidic or basic aqueous solvents
PCC: Pyridium Chlorochromate
Breathalyzers and Intoxilizers – used to detect CH3CH2OH on breath o The breathalyzer device contains: Two glass vials containing the chemical reaction mixture A system of photocells connected to a meter to measure the color change associated with the chemical reaction
Dess Martin Periodinane – another mild oxidant in dichloromethane solvent o 1° alcohol to aldehyde
6
CHM138H1 Jasmyn Lee
o 2° alcohol to ketone 1. Substitution reaction between the alcohol and the I(V) reagent to form a new periodinane intermediate 2. Expulsion of reduced I(III) as the leaving group
17.11 Spectroscopy of Alcohols and Phenols 12. 5 Spectroscopy and the Electromagnetic Spectrum Electromagnetic Spectrum: o Gamma rays, X rays, ultraviolet, visible, infrared, microwaves, radio waves 12.6 Infrared Spectroscopy Infrared (IR) Spectroscopy E = hν = hc (1/λ) Wavenumber – the number of waves per centimeter = cm-1; reciprocal of wavelength
Infrared radiation causes excited vibrations in molecules: o Stretching: Symmetric Asymmetric
o
o o o
Bending: In-plane
Out-of-plane
Stretching energies > bending energies Roughly 1015 vibrations/sec A molecule can stretch and bend only at a specific frequency, corresponding to specific energy levels When a molecule is irradiated with electromagnetic radiation, energy is absorbed if the frequency of the radiation matches the frequency of the vibration Causes increased amplitude for the vibration
7
CHM138H1 Jasmyn Lee
12.7 Interpreting Infrared Spectra Different functional groups vibrate at different energies, allowing identification of functional groups in a molecule The energies of many functional group vibrations are largely independent of the structure of the rest of the molecule Fingerprint Region – 1500 cm-1 – 400 cm-1
–O-H 3200 to 3600 cm-1 –C=O 1680 to 1800 cm-1 (strong, sharp) If there is a strong peak at 180 to 1800 cm-1, the molecule has a C=O group
8
CHM138H1 Jasmyn Lee If there is NO peak at 1680 to 1800 cm-1, the molecule DOES NOT have a C=O group If there is a peak at 3200 to 3600 cm-1, the molecule has an –O-H group If there is NO peak at 3200 to 2600 cm-1, the molecule DOES NOT have an –O-H group
Intoxilyzer 5000EN: AlcoBlow Following in the tradition of the intoxilyzer 4011 and the intoxilyzer 5000, the intoxilyzer 5000EN enhances the court-tested reliability and accuracy of evidential infrared spectrometry breath alcohol testing The intoxilyzer 5000EN is backed by CMI’s factory service and support The Intoxilyzer device uses IR spectroscopy:
9
