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NMR

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Chem 315 & Chem 318 Lab Review Notes ... Note: These items usually placed at the beginning of a lab report. ... upward from the yellow/blue flame area. ... – PowerPoint PPT presentation

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Title: NMR


1
  • NMR
  • Chemical Shift
  • Protons in a strong magnetic field will absorb
    Radio Frequency radiation at a specific frequency
    (Resonance).
  • The frequency of absorption (in Hz) relative to
    the frequency of the NMR instrument in MHz) is
    reported in units of PPM and is a function of the
    electromagnetic force required to induce the
    proton to resonate.
  • The resonance signal, reported in PPM, is plotted
    on the X-axis of the NMR chart. It location is
    referred to as the Chemical Shift.
  • Chemical Equivalence Protons having the same
    chemical and magnetic environment will produce
    one NMR signal.
  • The valence electrons in the vicinity of a proton
    provide Diamagnetic Shielding of the proton,
    i.e., the electron density about the proton.
  • Electronegative Groups decrease electron density
    by withdrawing electrons from the area around the
    proton thus less electromagnetic energy is
    required to induce resonance. The NMR signal thus
    moves down field increasing the Chemical Shift.
  • Electron Donating Groups donate electrons to the
    area around the proton, increasing electron
    density. Thus, the NMR signal moves upfield
    decreasing the Chemical Shift.
  • Spin Spin Splitting (the n1) rule
  • The number of peaks produced by equivalent
    Protons on a carbon atom is determined by the
    number of protons on the adjacent carbon
    atoms.Example Two protons on a carbon atom
    attached to two other carbon atoms with a total
    of 5 protons will act as a group to produce n1
    (516) peaks, i.e., a sextet.
  • Peak Areas Area under absorption peak is
    proportional to the number of protons present.
    Compute relative peak area by measuring the
    stairstep heights. See Pavia on page 915 or web
    site notes.
  • Look for Methyl groups around 1.0 PPM, Methylene
    Groups (CH2) around 2.0 PPM Aromatic Protons
    around 7.0 PPM. Aldehyde proton around 9.5 PPM
    Carboxylic Acid Proton around 10.5 PPM.
  • The presence of nearby Electronegative elements
    (Oxygen, Halogens, Nitrogen groups) will decrease
    the electron density causing the signal to move
    downfield, i,e,. increase the Chemical Shift.

2
  • NMR (Cont)
  • Aromatic Rings and other unsaturated molecules
  • Some proton types have chemical shifts not
    explained by the Electronegativity of the
    attached groups.
  • Aryl (benzene ring), Alkene (C), Alkyne (C ),
    and Aldehyde (OCH) related protons have
    resonance effects not expected from
    electron-withdrawing effects of electronegative
    elements.
  • The movement of ? electrons in an unsaturated
    molecule also generates a magnetic field that can
    influence the applied magnetic field.
  • The relative shielding and deshielding of protons
    in groups with ? electrons is dependent on the
    orientation of the molecule with respect to the
    applied magnetic field
  • Activating groups will add electron density and
    provide additional shielding of the protons.
  • Deactivating Groups will decrease electron
    density resulting in decreased shielding.
  • In a Benzene ring , the ? electrons are induced
    to circulate around the ring by the applied
    magnetic field, creating a ring current, which in
    turn produces a magnetic field further
    influencing the shielding of the ring protons.
  • The presence of ring current causes the applied
    magnetic field to become non-uniform (diamagnetic
    anisotropy) in the vicinity of the benzene ring.
  • The effect of the anisotropic field is to further
    deshield the benzene protons increasing the
    chemical shift. i.e., absorption signal moves to
    the left (downfield)on the chart.
  • Thus, protons attached to the benzene ring are
    influenced by three (3) magnetic fields
  • Strong Applied Magnetic Field
  • Normal Shielding by the Valence Electrons
  • Anisotropic Effect from Ring Current

3
  • NMR (Cont)
  • Protons on atoms other than Carbon atoms (acids,
    alcohols, amines, amides, etc) also produce
    Absorptions, usually singlets, with highly
    varying Chemical Shifts.
  • Carbon 13
  • Spin-Spin Splitting is different than in H1 NMR
  • The splitting peaks produced by a given carbon
    atom are based on the number of protons attached
    to that carbon atom.
  • Coupled Decoupled (protons removed) spectra.
  • Most Carbon atoms, except truly chemically
    equivalent carbons, produce unique absorptions
    thus, C-13 is mostly used to identify the number
    of unique carbon atoms in the molecule.
  • NMR Analysis Approach
  • Check for signal at Chemical Shift 9-10 ppm
    Aldehyde present
  • Check for signal at Chemical Shift 10-11 ppm
    Carboxylic Acid
  • Check for presence of Methyl groups at Chemical
    Shift in vicinity of 1.0 ppm.
  • The signal for a Methyl group may be moved
    downfield under the influence of an
    electronegative group or atom.
  • Look for peak area integration values near the
    signal. The value represents the relative number
    of protons on the carbon atom. If the value is a
    multiple of 3, there is more than one
    equivalent carbon atom involved, i.e., 2 or 3
    equivalent Methyl groups (Iso or Tertiary
    groups).
  • If the Methyl group signal is a multiplet, the
    number of peaks in the multiplet is equal to the
    total number of protons on the carbon atoms
    attached to the Methyl Carbon plus 1 (n1 rule).
  • There may be multiple Methyl groups present,
    some of which could be equivalent producing one
    signal (singlet or multiplet) and other
    non-unique Methyl groups each producing its own
    signal (singlet or multiplet).

4
  • NMR (Cont)
  • NMR Analysis Approach (Cont)
  • Check for the presence of Methylene groups.
  • The same process used to determine the number of
    Methyl groups is the same for Methylene
    groups, except here the Area Integration values
    would be multiples of 2.
  • The presence of Benzene rings is indicated by
    signals with Chemical Shifts of about 7.
  • The signals for Benzene rings are often complex
    because of the anisotropic effect of the ring
    current and substitution patterns on the ring.
  • The Area integration value often gives some idea
    of how many of the six (6) ring protons have been
    substituted.
  • There may be other singlets not associated with
    the Methyl or Methylene groups that are
    associated with protons attached to atoms other
    than carbon OH, NH, NH2, etc.
  • If available
  • Evaluate the IR for functional groups present.
  • Evaluate the Mass Spectra for the Molecular
    Weight and the presence of Chlorine (2 peaks, 31
    abundance ratio), Bromine (2 peaks, 11 abundance
    ratio), or Nitrogen where the Molecular Ion Peak
    value is Odd.
  • Assemble the various fragments into possible
    compound configurations.

5
  • NMR (Cont)
  • NMR Analysis Approach (Cont)
  • NMR Analysis Example
    2-Phenylbutane

Note Each of the fragments has one or more
unresolved sigma bonds. Try matching
an unresolved bond in one fragment with an
unresolved bond in another fragment.
Some fragments may be accounted for as
partial fragments of other
fragments. If any unresolved bonds
persist, check the molecular weight to see a
symmetrical molecule might be involved.
6
  • Infrared Spectrophotometry (IR)
  • Principal Absorptions
  • Carbonyl Group - 1715 cm-1 (Aldehydes, Ketones,
    Acids, Esters, Amides, Anhydrides)
  • C-O - 1000 - 1300 cm-1 (Alcohols, Ethers,
    Esters, Acids)
  • Saturated - C-H (Alkanes) - Right side of 3000
    cm-1
  • Unsaturated - C-H (Alkenes) - Left side of
    3000 cm-1
  • Unsaturated - Aromatic versus Alkenes
  • Aromatic - Overtone area
    1667 to 2000 cm-1 Out of Plane (OOP)
    690 to 900 cm-1 4 sharp
    absorptions in pairs 1450 to 1600 cm-1
  • Alkynes - CC (2150 cm-1) C--H (Terminal)
    (3300 cm-1)
  • Nitriles - CN (2250 cm-1)
  • Nitro (NO2) - 1300 1390 cm-1 1500 to 1600
    cm-1
  • Amines - 3300 to 3500 cm-1 Primary Amine (Two
    Bands) Secondary Amine (One Band, often weak)
    Tertiary Amine (No Absorptions)
  • Analysis Approach
  • Carbonyl Group - Confirm presence or absence of
    Carbonyl (CO) group, a strong absorption at
    about 1715 cm-1, actual range could be from 1600
    1820 cm-1.
  • Saturation / Unsaturation
  • Saturation - Confirm presence or absence of
    saturated alkane(-C-H) structures, i.e.,
    multiple absorptions between 2900 3000 cm-1.
  • Unsaturation - Confirm presence or absence of
    unsaturated(C-H) structures, i.e., multiple
    absorptions between 3100 3000 cm-1.

7
  • Determine whether unsaturated structures belong
    to alkene or aromatic structures.
  • Aromaticity is confirmed as follows
  • 1- 4 weak absorptions in aromatic overtone region
    from 1700 2000 cm-1
  • 4 sharp absorptions that occur in pairs from 1450
    1600 cm-1.
  • Out of Plane (OOP) bending occurs at 690 900
    cm-1.
  • Determine substitution patterns on benzene ring
    using table on page 897 of the Pavia text.
  • Alkene structures are confirmed as follows
  • Out of plane (OOP) bending from 650 1000 cm-1
  • CC stretch from 1600 -1675 cm-1
  • Determine substitution patterns on the alkene
    structures from table on page 895 of the Pavia
    text.
  • Hydroxyl (OH) group
  • Alcohols / Phenols Stretch (sharp peak) from
    3600 - 3650 cm-1
  • Acids Stretch, usually very broad (from
    hydrogen bonds) at2500 - 3300 cm-1
  • C-O group
  • Alcohols Stretch in range of 1000 1300 cm-1
  • Ethers Stretch in range of 1000 1300 cm-1
  • Esters Stretch (sometimes 2) in range of
    1000 1300 cm-1
  • Amines
  • N-H Stretch occurs in the range 3300 3500 cm-1.

8
  • Nitro Compounds
  • NO stretch is usually two strong bands at 1300
    -1390 cm-1 1500 1600 cm-1
  • Nitriles
  • CN stretch (sharp) absorption near 2250 cm-1
  • Alkynes
  • C-H (terminal alkyne) stretch (sharp) is usually
    near 3300 cm-1
  • C-CC-C stretch (sharp) is usually near 2150
    cm-1

9
  • Mass Spectrometry
  • Mass Spectrum with Molecular Ion Peak(s).Note
    Sometimes the Mass Spectrum is not given, just
    the value(s) for the Molecular Ion
    peak (M).
  • Molecular Ion Peak (M)
  • Peak(s) farthest to the right on the Mass
    Spectrum
  • Represents the Molecular Weight
  • Molecular Ion peak values that are Odd indicate
    the presence of an Odd number of Nitrogen atoms
    in the compound
  • Two Molecular Ion peaks with a relative abundance
    ratio of 31 indicate the presence of a single
    Chlorine
  • Two Molecular Ion peaks with a relative abundance
    ratio of 11 indicate the presence of a single
    Bromine.
  • Ultraviolet Visual Spectrometry
  • UV-Vis Molar Absorptivity (Molar Extinction
    Coefficient ? log ?
  • Conjugate systems (alternating double bonds -
    ?,? - Unsaturated ketones, Dienes,
    Polyenes)show values of ? log ? in the
    range ? 10,000 100,000 (Log ?
    4 5)
  • Aromatic Conjugated Systems show values of ? and
    log ? in the range ? 1000 10,000
    (Log ? 3 4)
  • Carbonyl (CO) compounds show values of ? and log
    ? in the range ? 10 100
    (Log ? 1.5 2.5)
  • Nitro (-1ON O) compounds show values of ? in
    the range ? lt10
    ( Log ? lt 1.0)

10
  • Partial Elemental Analysis
  • A partial elemental analysis of the compound
    usually provides Carbon
    Hydrogen.
  • The student must complete this analysis and give
    the Molecular Formula of the compound.
  • Example From the Mass Spectrum the Molecular
    Weight is 58.080
    C - 62.0 H 10.4
  • 0.620 58.080 36.03 / 12.01
    ?3 ? 3 Carbons atoms
  • 0.104 58.080 6.05 / 1.001
    ?6 ? 6 Hydrogen atoms
  • Determine mass of remaining elements in the
    compound
  • 58.080 (36.03 6.05) 15.95
    16 ? 1 Oxygen
  • ? Molecular Formula C3H6O
  • Note The molecular ion peak(s), molar
    absorptivity coefficient (from UV- VIS), and
    the principal functional groups from the IR
    provide the information necessary to
    identify any additional elements present in
    the compound.

11
  • The Laboratory Process
  • Know the Stoichiometric Reactions and the
    Reaction Mechanisms.
  • All synthesis experiments require the
    determination of reactant masses, moles,
    stoichiometric molar ratios, limiting reagent,
    and theoretical yield.
  • Note These items usually placed at the beginning
    of a lab report.
  • Products are sometimes purified by
    Recrystallization
  • Note Know the details of this process and the
    properties of a good solvent.
  • Unknown Liquids are usually first purified by
    Simple Distillation
  • Describe the data collection process in Simple
    Distillation to explain how the pure component
    is separated from the impurities.
  • Explain why measured boiling points usually dont
    match the literature boiling points.
  • Intermediate product mixtures are often washed
    or extracted
  • Explain the Extraction process
  • What equipment is used?
  • What reagents were used?
  • What is venting
  • Did product change phases?
  • The Refractive Index is determined for most
    organic liquids, either unknowns or synthesized
    products.
  • How is the measured value corrected for
    temperature?
  • ND20 NDRT ?t ( 0.00045)
  • ?t Room Temp (RT) - 20

12
  • The Chem 315 Experiments
  • Melting Point Refractive Index
  • Melting Point
  • Define Melting Point
  • What is melting point range?
  • What happens to the melting point and melting
    point range of a mixture as the concentration of
    one of the compounds increases relative to the
    concentration of the other compounds in the
    mixture?
  • What is the relationship between the amount of
    contaminant in a mixture and the Eutectic Point
  • Refractive Index
  • Define Refractive Index
  • What is the impact of temperature on Refractive
    Index?
  • How is the measured value corrected for
    temperature?
  • Recrystallization
  • What is the purpose of Recrystallization?
  • Distinguish between Recrystallization and
    Precipitation.
  • What constitutes a Good solvent know at least
    5 properties.
  • Describe the recrystallization process.

13
  • The Chem 315 Experiments (Cont)
  • Gas Chromatography Acetate Mixture
  • What are the principles of separation in Gas
    Chromatography?
  • Liquid Phase
  • Carrier Gas
  • Moving Gas Phase
  • Stationary Liquid Phase
  • Time a compound stays in the Vapor Phase is a
    function of the Vapor Pressure of the compound.
  • The more volatile (Low Boiling Point / Higher
    Vapor Pressure) compounds arrive at the end of
    the column first and pass into the detector.
  • What are the factors affecting the separation of
    compounds?
  • Boiling Points (vapor pressure) of compounds.
  • Flow Rate of Carrier Gas.
  • Choice of Liquid Phase Molecular weights,
    functional groups, and polarities of component
    molecules are factors in selecting liquid phase.
  • Length of Column Similar compounds require
    longer columns than dissimilar compounds.
    Isomeric mixtures often require quite long
    columns.
  • What is retention Time?
  • The period following injection that is required
    for a compound to pass through the column to the
    point where the detector current is maximum, i.e.
    maximum pen deflection or maximum peak height.
  • For a given set of constant conditions (carrier
    gas, flow rate of carrier gas, column
    temperature, column length, liquid phase,
    injection port temperature), the retention time
    of any given compound is always constant.

14
  • The Chem 315 Experiments (Cont)
  • Gas Chromatography Acetate Mixture (Cont)
  • What is the relationship between the area under a
    Gas Chromatography peak and the Mole content of
    the mixture?
  • The area under a gas chromatograph peak is
    proportional to the amount (moles) of the
    compounds eluted.
  • The molar percentage composition of a mixture can
    be approximated by comparing the relative areas
    of the peaks in the chromatogram.
  • This method assumes that the detector is equally
    sensitive to all compounds and its response is
    linear.
  • Triangulation Method of Determining Area Under
    Peak.
  • Multiply the height of peak (in mm) above the
    baseline by the width of the peak at half the
    height.
  • The Baseline is a straight line connecting
    side arms of the peak. Best if peaks
    are symmetrical.
  • Add all of the areas to get the total area.
  • Divide each area by total area to get mole
    fraction.

15
  • The Chem 315 Experiments (Cont)
  • Simple Fractional Distillation
  • Pure Substance
  • Temperature remains constant during distillation
    process so long as both vapor and liquid are
    present
  • Liquid Mixture
  • Temperature increases throughout process because
    composition of vapor changes continuously.
  • Composition of vapor in equilibrium with the
    heated solution is different from the composition
    of the solution.
  • What is Simple Distillation?
  • Single vaporization- condensation cycle of a
    mixture that produces a distillate that is always
    impure at any temperature range between the range
    of boiling points of the components.
  • What is Fractional Distillation?
  • Accomplishes the same thing as multiple simple
    sequential vaporization-condensation cycles, by
    inserting a Fractionating Column between the
    Distillation Flask and the Distilling Head.
  • Gas Chromatography of Distillates
  • Determine the Mole of the original sample
    mixture and the fractions obtained from the
    Simple Fractional Distillations along using Gas
    Chromatography and Refractive Index.
  • Compare the Mole results obtained from the
    three methods with an evaluation of the best
    method to physically separate the mixture
    components and determine the Mole composition of
    the mixture.

16
  • The Chem 315 Experiments (Cont)
  • Synthesis of t-Butyl Chloride
  • Reaction of t-Butyl Alcohol (or t-Pentyl Alcohol)
    with conc. HCL to form t-Butyl Chloride (or
    t-Pentyl Chloride).
  • Stoichiometric Equation and Reaction Mechanism
  • Three-step Sn1 Nucleophilic Substitution
    Reaction.
  • This is a First Order Rate Reaction where the
    Rate of Formation of t-Butyl Chloride (t-Pentyl
    Chloride) is dependent only on the concentration
    of the Alcohol it is independent of the amount
    of acid (HCL) used.
  • The yield (mass or moles) of the washed and
    driedt-Butyl (t-Pentyl) Chloride product is
    compared to the theoretical amount of product
    expected, which is computed from a Limiting
    Reagent calculation using the Stoichiometric
    Molar Ratio.
  • The Limiting Reagent is that reactant whose
    mass (on a molar equivalent basis) is totally
    consumed in the reaction leaving an excess of the
    other reactant.
  • The Limiting Reagent, thus, determines the
    maximum amount (in moles) of product that can be
    expected.

17
  • The Chem 315 Experiments (Cont)
  • Qualitative Organic Analyses
  • Solubility (H2O, H2SO4)
  • Beilstein (Flame) for Alkyl Aryl Halides
  • Silver Nitrate/Ethanol (Sn1 reaction) for Alkyl
    Aryl Halides
  • Compounds equipped with good leaving groups (H2O,
    CL, Br, I)
  • Compounds that can form stable carbocations
  • Benzyl gt Allyl gt Tertiary (3o) gt
    Secondary (2o) gt
  • Primary (1o) gt Methyl gt Vinyl gt Aryl
    (Aromatic).
  • Allyl, Benzyl, Tertiary Halides give positive
    test (White PPT).
  • Primary Secondary Alkyl Halides test positive
    when heated (100oC).
  • Aromatic and many Vinyl Substituted Halides do
    not give positive tests.
  • Sodium Iodide/Acetone (Sn2 reaction) for Alkyl
    Aryl Halides
  • Relative Halide reactivity for an Sn2 reaction is
    the opposite of an Sn1 reaction, that is
  • Vinyl gt Methyl gt Primary (1o) gt Secondary (2o) gt
    Tertiary (3o) gt Allyl gt Benzyl gt Aryl
    (Aromatic)
  • Primary Alkyl Chlorides and Bromides would react
    with the Sodium Iodide in a reaction to
    substitute the Chloride Bromide ions with the
    Iodide ions. An immediate precipitate is formed.
  • Secondary Alkyl Halides will give a precipitate
    when heated to 50oC and then cooled.
  • Tertiary Alkyl Halides will also give a
    precipitate when heated to 50oC and then cooled.
  • Unreactive Aryl (Benzyl and Aromatic) Chlorides
    Bromides would not produce a reaction even after
    heating, thus no precipitate.

18
  • The Chem 315 Experiments (Cont)
  • Qualitative Organic Analyses (Cont)
  • Bromine/Methylene Chloride for Unsaturated CC
    CC
  • Addition reaction of Bromine (Br2), a red liquid,
    to a compound containing a double or triple bond
    produces a colorless Dibromide.
  • The double (or triple bond) must be sufficiently
    electron-rich to initiate the reaction.
    Therefore, minimal electron withdrawing groups
    (Deactivators), such as Carboxyl Groups attached
    to molecule, would hinder the reaction.
  • Unsubstituted Aromatic compounds do not react
    with the Bromine reagent.
  • Even if the ring has substituted activating
    groups (donate electrons to the ring) the
    reaction would be a substitution and not an
    addition.
  • KMnO4 (Baeyer Test) for Unsaturated CC CC
  • Potassium Permanganate (KMNO4) (Purple Color) is
    an oxidizing agent.
  • Following the oxidation of an unsaturated
    compound, the Permanganate ion is reduced to
    Manganese Dioxide (MnO4), a brown precipitate.
  • Note Other easily oxidized compounds
    Aldehydes, some Alcohols, Phenols, and Aromatic
    Amines should be accounted for in your
    analysis.
  • Ignition for Aromatic CC bonds
  • Positive test is a sooty yellow flame.
  • Note The Sooty flame usually comes off
    fairly quickly. Look for it moving
    quickly away and upward from the
    yellow/blue flame area.
  • Positive test is indicative of a high degree of
    Unsaturation and is probably Aromatic

19
  • The Chem 315 Experiments (Cont)
  • Qualitative Organic Analyses (Cont)
  • Acetyl Chloride for Alcohols
  • Acid Chlorides react with Alcohols to form
    esters.
  • Acetyl Chloride forms Acetate esters.
  • This test does not work well with solid alcohols.
  • Positive test is evolution of Heat and Hydrogen
    Chloride (HCl) gas.
  • Phenols also react with Acetyl Chloride and
    should be eliminated prior to testing for
    Alcohols.
  • Amines also react with Acetyl Chloride to produce
    heat and also should be eliminated prior to
    testing.
  • Lucas Test for Alcohols
  • Primary Alcohols dissolve in reagent giving clear
    solution.
  • Secondary Alcohols produce cloudiness after about
    3-5 minutes. May need to heat slightly.
  • Tertiary, Benzylic, and Allylic alcohols produce
    immediate cloudiness eventually, an immiscible
    Alkyl Halide separates into a separate layer.
  • Chromic Acid for Alcohols
  • Distinguish Primary Secondary Alcohols from
    Tertiary Alcohols.
  • Chromic Acid (Cr6) oxidizes Primary and
    Secondary Alcohols to Carboxylic Acids and
    Ketones, respectively.
  • Chromium (6) - orange is reduced to Chromium
    (3) green.
  • Tertiary Alcohols do not react with Chromic Acid.

20
  • The Chem 318 Experiments
  • Bromination of Toluene
  • Electrophilic Aromatic Substitution
  • The Methyl group is electron donating (ring
    activating) favors O/P subst.
  • Meta vs Ortho/Para Substitution Which prevails
    in this experiment and why?
  • Positively charged Bromine Cations (the
    Electrophile) how are the Bromine cations
    produced, i.e., the reaction between Bromine and
    Iron (Fe)
  • Nitration of Methyl Benzoate
  • Carbo-Methoxy group is electron withdrawing
    therefore it favors Meta substitution of the
    Nitronium ions - Why?
  • Reaction producing the Nitronium Ions (H2SO4
    HNO3.
  • Water Impact of too much water in reaction.
  • Temperature Keep low or high Why?
  • Grignard
  • Bromobenzene Magnesium ? Phenyl Magnesium
    Bromide
  • Grignard CO2 (Electrophile) ? Benzoic Acid
  • Grignard Ketone ? Tertiary Alcohol
  • Grignard Aldehyde ? Secondary Alcohol
  • Grignard Formaldehyde ? Primary Alcohol
  • Function of Ether (Stabilize the Grignard)
  • Impact of too much heat (Production of Biphenyl)

21
  • The Chem 318 Experiments (Cont)
  • Qualitative Analysis
  • Classification Tests for Aldehydes Ketones
  • Solubility in Water - Insoluble gt 5 Carbons
  • Solubility in H2SO4 - Most Aldehydes Ketones
  • 2,4-Dimethylphenylhydrazine - Aldehydes Ketones
  • Yellow ppt Unconjugated Red ppt
    Highly Conjugated
  • Chromic Acid - Reduction of Cr 6 (orange)
    to Cr3 (green ppt) for Aldehydes Note
    Primary Secondary Alcohols, which must be
    eliminated first, also test positive.
  • Tollins Reagent - Silver Mirror for
    Aldehydes Note Secondary Alcohols with
    Alpha Carbon adjacent to Carbonyl also test
    positive.
  • Iodoform Test - Yellow ppt for Methyl
    Ketones Note Acetaldehyde Sec Alcohols
    with Alpha Carbon adjacent to Carbonyl also
    test positive.
  • Synthesis of Iso-Pentyl Acetate (Banana Oil)
  • Acid Catalyzed Esterification
  • Excess Acetic acid required to maximize yield,
    i.e., move equilibrium to right.
  • Purpose of washing with Sodium Bicarbonate
    Remove Acid
  • Purpose of washing with Satd Sodium Chloride
    Remove Water

22
  • The Chem 318 Experiments (Cont)
  • Dibenzalacetone
  • Claisen-Schmidt Reaction involving formation of
    an Enolate ion.
  • Two moles Benzaldehyde react with 1 mole acetone
    to form 1 mole of Dibenzalacetone.
  • The Molar ratio of Benzaldehyde to Acetone is
    21, which must be taken into account when
    determining the Limiting Reagent.
  • Product is washed with distilled water to remove
    all traces of Sodium Hydroxide.
  • Acetanilide
  • Amines vs Amides Amines are weakly basic and
    Amides are less basic than Amines.
  • Amides stronger acidity is related to the strong
    electron withdrawing effect of the Carbonyl
    Oxygen.
  • Amines are easily oxidized, but can be protected
    by first converting them to an Amide.
  • The Synthesis of Acetanilide, an Amide, from
    Aniline, an Amine, is by Nucleophilic Acyl
    Substitution, an Addition/Elimination reaction.
  • Acetic Anhydride acts as the positively charged
    (Carbonyl Carbon) Electrophile.
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