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CH223 Organic Chemistry II Phone : 869-2835, e-mail : leehy @kaist.ac.kr Office : 자연과학동 화학과 (E6-4) 410

CH223 Organic Chemistry II Phone : 869-2835, e-mail : leehy @kaist.ac.kr Office : 자연과학동 화학과 (E6-4) 4104 호실 lecture notes website : http://org.kaist.ac.kr / Main textbook : Organic Chemistry, 2nd ed. by Janice Gorzynski Smith

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CH223 Organic Chemistry II Phone : 869-2835, e-mail : leehy @kaist.ac.kr Office : 자연과학동 화학과 (E6-4) 410

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  1. CH223 Organic Chemistry II • Phone : 869-2835, e-mail : leehy@kaist.ac.kr • Office : 자연과학동 화학과(E6-4) 4104호실 • lecture notes website : http://org.kaist.ac.kr/ • Main textbook : Organic Chemistry, 2nd ed. • by Janice Gorzynski Smith • Auxiliary textbook : Advanced Organic Chemistry, 4th ed. by F. Carey and R. Sundberg • Evaluation Criteria • Final exam : about 25%, midterm exam : about 25%, • Quiz (4 times)  : about 40% • Homework : about 5%  • Attendance : about 5% • Practice Hour : Thursday 7:00 – 9:00 TA’s : Kim Jinho (409) • ~ 40minutes of class review Kim Yubin (410) • ~ 40 minutes of homework review, problem solving, Q&A • ( ~ 40 minutes of Quiz )

  2. Lecture Schedule 1st week : Mass Spectroscopy and Infrared Spectroscopy (Chap 13) 2nd week : Nuclear Magnetic Resonance Spectroscopy (Chap 14) 3rd week : Radical Reactions (Chap 15),1st Quiz 4th week : Conjugation, Resonance and Dienes (Chap 16) 5th week : Benzene and aromatic compounds (Chap 17) 6th week : Electrophilic aromatic substitution (Chap 18),2nd Quiz 7th week : Carboxylic acids and the acidity of the O-H bond (Chap 19) 8th week : Midterm Exam. 9th week : Introduction to carbonyl chemistry (Chap 20) 10th week :carbonyl chemistry (Chap 20), Aldehydes and ketones (Chap 21) 11th week : Aldehydes and ketones (Chap 21), 3rd Quiz 12th week : Carboxylic acids and their derivatives (Chap 22) 13th week : (Chap 22), Substitution reactions of carbonyl compounds at the a carbon (Chap 23) 14th week : (Chap 23), Carbonyl condensation reactions (Chap 24), 4th Quiz 15th week : Carbonyl condensation reactions (Chap 24) 16th week : Final Exam

  3. Chapter 13 Mass Spectrometry & Infrared Spectroscopy

  4. Mass Spectrometry Introduction • Mass spectrometry is a technique used for measuring the molecular weight and determining the molecular formula of an organic compound (including biomolecule).

  5. Mass Spectrometry Introduction • Mass spectrometry is a technique used for measuring the molecular weight and determining the molecular formula of an organic compound (including biomolecule). • In a mass spectrometer, a molecule is vaporized and ionized by bombardment with a beam of high-energy electrons. ~ 1600 kcal (or 70 eV). cf. s bond ~100 kcal molecular ion (parent ion)

  6. The mass spectrometer analyzes the masses of cations. • A mass spectrum is a plot of the amount of each cation (its relative abundance) versus its mass to charge ratio (m/z, where m is mass, and z is charge). • Since z is almost always +1, m/z actually measures the mass (m) of the individual ions. • A mass spectrometer analyzes the masses of individual molecules, not the weighted average mass of a group of molecuels.

  7. Mass Spectrometry Mass spectrum of hexane (CH3CH2CH2CH2CH2CH3)

  8. Analyzing Unknowns using the molecular ions • Hydrocarbons like methane (CH4) and hexane (C6H14), as well as compounds that contain only C, H, and O atoms, always have a molecular ion with an even mass. • nitrogen rule: A compound that contains an odd number of N atoms gives an odd molecular ion. A compound that contains an even number of N atoms (including zero) gives an even molecular ion.

  9. Alkyl Halides and the M + 2 Peak • A mass spectrometer analyzes the masses of individual molecules, not the weighted average mass of a group of molecuels. • Most elements have one major isotope. • Chlorine has two common isotopes, 35Cl and 37Cl, which occur naturally in a 3:1 ratio. • Thus, there are two peaks in a 3:1 ratio for the molecular ion of an alkyl chloride. • The larger peak, the M peak, corresponds to the compound containing the 35Cl. The smaller peak, the M + 2 peak, corresponds to the compound containing 37Cl. • Thus, when the molecular ion consists of two peaks (M and M + 2) in a 3:1 ratio, a Cl atom is present. • Br has two isotopes—79Br and 81Br, in a ratio of ~1:1. Thus, when the molecular ion consists of two peaks (M and M + 2) in a 1:1 ratio, a Br atom is present.

  10. Mass Spectrometry Alkyl Halides and the M + 2 Peak If a compound contains two chlorine atoms, MS shows M : M+2 : M+4 = 9:6:1

  11. Mass Spectrometry Alkyl Halides and the M + 2 Peak If a compound contains two bromine atoms, MS shows M : M+2 : M+4 = 1:2:1

  12. Mass Spectrometry High Resolution Mass Spectrometers • Low resolution mass spectrometers report m/z values to the nearest whole number. Thus, the mass of a given molecular ion can correspond to many different molecular formulas. • High resolution mass spectrometers measure m/z ratios to four (or more) decimal places. m/z = 60

  13. Gas Chromatography—Mass Spectrometry (GC-MS) • The GC-MS records a gas chromatogram of the mixture, and yields a plot of the amount of each component versus its retention time (the time required to travel through the column), and its molecular ion in the mass spectrum. Valuable tool in doping test and drug analysis

  14. Infrared Spectroscopy Electromagnetic Radiation • The different forms of electromagnetic radiation make up the electromagnetic spectrum.

  15. Infrared Spectroscopy Electromagnetic Radiation • Frequency and wavelength are inversely proportional ( = c/). Thus, energy and wavelength are inversely proportional. • E increases as  increases • E decreases as  increases E = h= hc/ • When electromagnetic radiation strikes a molecule, some wavelengths, but not all, are absorbed. • For absorption to occur, the energy of the photon must match the difference between two energy states in the molecule. • The larger the energy difference between two states, the higher the energy of radiation needed for absorption, the higher the frequency, and the shorter the wavelength.

  16. Infrared Spectroscopy Background • Infrared (IR) spectroscopy is used to identify the functional groups in a compound. • IR radiation is the energy source used in IR spectroscopy. • Frequencies in IR spectroscopy are reported using a unit called wavenumber (): ~ ~  = 1/ • Wavenumber is inversely proportional to wavelength and is reported in reciprocal centimeters (cm–1). • Frequency (and therefore, energy) increases as the wavenumber increases. • Using the wavenumber scale, IR absorptions occur from 4000 cm–1– 400 cm–1.

  17. Infrared Spectroscopy Background • Absorption of IR light causes changes in the vibrational motions of a molecule. • The different vibrational modes available to a molecule include stretching and bending modes. • The vibrational modes of a molecule are quantized, so they occur only at specific frequencies which correspond to the frequency of IR light.

  18. Infrared Spectroscopy Background • When the frequency of IR light matches the frequency of a particular vibrational mode, the IR light is absorbed, causing the amplitude of the particular bond stretch or bond bend to increase.

  19. Infrared Spectroscopy Characteristics of an IR Spectrum • In an IR spectrometer, light passes through a sample. • Frequencies that match the vibrational frequencies are absorbed, and the remaining light is transmitted to a detector. • An IR spectrum is a plot of the amount of transmitted light versus its wavenumber.

  20. Infrared Spectroscopy Characteristics of an IR Spectrum—1-Propanol Wavenumber, frequency and energy decrease from left to right.

  21. Infrared Spectroscopy Characteristics of an Infrared Spectrum • The IR spectrum is divided into two regions: the functional group region (at  1500 cm-1), and the fingerprint region (at < 1500 cm-1).

  22. Infrared Spectroscopy IR Absorptions • Where a particular bond absorbs in the IR depends on bond strength and atom mass. • Hooke’s Law describes the relationship of frequency to mass and bond length.

  23. Infrared Spectroscopy IR Absorptions • Bonds absorb in four predictable regions of an IR spectrum.

  24. Infrared Spectroscopy IR Absorptions

  25. Infrared Spectroscopy IR Absorptions • Even subtle differences that affect bond strength affect the frequency of an IR absorption. • The higher the percent s-character, the stronger the bond and the higher the wavenumber of absorption.

  26. Infrared Spectroscopy IR Absorptions

  27. Infrared Spectroscopy IR Absorptions • For a bond to absorb in the IR, there must be a change in dipole moment during the vibration. • Symmetrical nonpolar bonds do not absorb in the IR. This type of vibration is said to be IR inactive.

  28. Infrared Spectroscopy IR Absorptions in Hydrocarbons Hexane has only C-C single bonds and sp3 hybridized C atoms. Therefore it has only one major absorption at 3000-2850 cm-1.

  29. Infrared Spectroscopy IR Absorptions in Hydrocarbons 1-Hexene has a C=C and Csp2-H, in addition to sp3 hybridized C atoms. Therefore, there are three major absorptions: Csp2-H at 3150-3000 cm-1; Csp3-H at 3000-2850 cm-1; C=C at 1650 cm-1.

  30. Infrared Spectroscopy IR Absorptions in Hydrocarbons 1-Hexyne has a CC and Csp-H, in addition to sp3 hybridized C atoms. Therefore, there are three major absorptions: Csp-H at 3300 cm-1; Csp3-H at 3000-2850 cm-1; CC at 2250 cm-1.

  31. Infrared Spectroscopy IR Absorptions in Oxygen Containing Compounds The OH group of the alcohol shows a strong absorption at 3600-3200 cm-1. The peak at ~3000 cm-1 is due to sp3 hybridized C—H bonds.

  32. Infrared Spectroscopy IR Absorptions in Oxygen Containing Compounds The C=O group in the ketone shows a strong absorption at ~1700 cm-1. The peak at ~3000 cm-1 is due to sp3 hybridized C—H bonds.

  33. Infrared Spectroscopy IR Absorptions in Oxygen Containing Compounds The ether has neither an OH or a C=O, so its only absorption above 1500 cm-1 occurs at ~3000 cm-1, due to sp3 hybridized C—H bonds.

  34. Infrared Spectroscopy IR Absorptions in Nitrogen Containing Compounds The N—H bonds in the amine give rise to two weak absorptions at 3300 and 3400 cm-1.

  35. Infrared Spectroscopy IR Absorptions in Nitrogen Containing Compounds The amide exhibits absorptions above 1500 cm-1 for both its N—H and C=O groups: N—H (two peaks) at 3200 and 3400 cm-1; C=O at 1660 cm-1.

  36. Infrared Spectroscopy IR Absorptions in Nitrogen Containing Compounds The CN of the nitrile absorbs in the triple bond region at ~2250 cm-1.

  37. IR and Structure Determination Structural elucidation of penicillin Proposed by Robinson based on model compound Proposed by Woodward based on IR (~1760cm-1) Confirmation of the reaction

  38. Infrared Spectroscopy IR and Structure Determination

  39. Infrared Spectroscopy IR and Structure Determination

  40. Homework 13.19, 13.21, 13.23, 13.24, 13.27, 13.32, 13.34, 13.35, 13.40, 13.41 42

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