Métodos espectroscópicos de análise (2014)

Apresentação em tema: "Métodos espectroscópicos de análise (2014)"— Transcrição da apresentação:

1 Métodos espectroscópicos de análise (2014)
QFL-4030 Métodos espectroscópicos de análise (2014) Home Page: (courses)

2 2nd ed. Saunders College Publishing.
Literatura Silverstein, R. M., Webster, F. X. and Kiemle, D. J. (2005) Spectrometric identification of organic compounds, 7th ed. J. Wiley & Sons. Pavia, D. L., Lampman, G. M., Kriz, G. S. (1996). Introduction to spectroscopy. 2nd ed. Saunders College Publishing. Modern Instrumental Techniques for Schools and Colleges Royal Society of Chemistry – Advancing the Chemical Sciences:

3 Objetivos Apresentar os fundamentos básicos e as aplicações dos principais métodos espectroscópicos utilizados em análise química estrutural, de modo a capacitar os alunos a interpretar espectros.

4 Programa Espectroscopia no UV-vis, infravermelho (IV),
espectrometria de massas e ressonância magnética nuclear.

5 Quinina: Pelletier e Magendie, 1820 Atropina: Mein, 1831.
Discovery of organic compounds was primarily motivated by bioactivity and their structural determination was based mostly on degradative reactions Morfina: Sertürner, 1805 Quinina: Pelletier e Magendie, 1820 Atropina: Mein, 1831. Papaverina: Merck, 1848. Cocaína: Wöhler, 1859. Escopolamina: Landenburg, 1881. Efedrina: Nagai, 1885. Tubocurarina: Boehm , 1895. Insulina: Abel, 1929.

6 Penicilina: Fleming, 1929. Dicumarol: Link, 1941. Cloranfenicol: Burkholder, 1947. Reserpina: Müller, 1952. Prostaglandinas: Bergströn, 1962. Encefalinas: Hughes, 1975.

7 Uso como antimalárico: Desde 1638
Isolamento: 1820 por Pelletier e Caventou Síntese: 1944 por Woodward

8 Determinação estrutural da quinina por
reações de degradação

9 Confirmadas por síntese dos fragmentos obtidos

10 Quinine (natural antimalarial compound) Synthetic derivatives:
Cinchona officinalis (quinine bark - Rubiaceae) Synthetic derivatives: Mefloquine (Lariam, Mefaquin) This quinine analog developed at Walter Reed Army Institute of Research (USA) and was used for the prophylaxis of malaria and also for treatment of chloroquine-resistant falciparum type. Primaquine Is used to treat malaria caused by P. vivax and P. ovale. It should be used in association with chloroquine or mefloquine to provide a complete cure. It is also used to treat fungal infections caused by Pneumocystis pneumonia, common in patients with AIDS.

11 Composição (tipos e quantidade de átomos): AE Rotação: Micro-ondas
Como diferenciar uma molécula de outra? Ponto de fusão, índice de refração, forma, tamanho, etc… Massa: EM Composição (tipos e quantidade de átomos): AE Rotação: Micro-ondas Vibração: Infravermelho Orbitais moleculares: UV-Vis Organização em cristais: Difração de raios X Estados de spin (mediante campo magnético): RMN

12 Análise elementar – Determinação fórmula mínima
CxHyOz + O2 (excesso) = x CO2 + y/2 H2O 9.83 mg mg mg Fórmula mínima CxHyOz, x = 64.6%; y = 10.8%; z = 24.6% C7H14O2

13 Vibrational transitions Bond breaking Eletronic transitions
Nuclear spin transitions energy EM UV-VIS IV RMN frequency

14 Comparação do comprimento de onda

15 General scheme for structural elucidation of natural compounds

16 CxHyOz C4H6O MM = 70 u.a. CC C-H OH C-O C-H CH2 OH CH2 CH -18 (OH)
𝐼=𝐶 − 𝐻 2 − 𝑋 2 + 𝑁 2 +1=2 CC C-H OH C-O C-H CH2 OH CH2 CH

17 Análise funcional orgânica
Determinação de grupos funcionais: Análise funcional orgânica Espectrofotometria no Ultravioleta e infravermelho

18

19 Infrared radiation λ = 2.5 to 17 μm n (número de onda) = 4000 to 600 cm-1 These frequencies match the frequencies of covalent bond stretching and bending vibrations. Infrared spectroscopy can be used to find out about covalent bonds in molecules. IR is used to tell: 1. what type of bonds are present 2. some structural information

20 Infrared n Converted in Vibrational energy in molecules Depends on:
10,000 cm-1 to 100 cm-1 Converted in Vibrational energy in molecules Vibrational Spectra appears as bands instead of sharp lines => as it is accompanied by a number of rotational changes Wave Number => n (cm-1) => proportional to energy Older system uses the wavelenght l (mm => 10-6 m) cm-1 = 104 / mm n Depends on: Relative masses of atoms Force constant of bonds Geometry of atoms

21 Lei de Hooke

22

23 Instrumentação

24 IR source è sample è prism è detector
graph of % transmission vs. frequency => IR spectrum 100 %T v (cm-1)

25 Intensity in IR Intensity: Transmittance (T) or %T T = I I0
Absorbance (A) A = log I I0 IR : Plot of %IR that passes through a sample (transmittance) vs Wavelenght

26 Instrumentação

27 Espectro no IV

28 Infrared Position, Intensity and Shape of bands gives clues on Structure of molecules Modern IR uses Michelson Interferometer => involves computer, and Fourier Transform (FTIR) Sampling => plates, polished windows, Films … Must be transparent in IR NaCl, KCl : Cheap, easy to polish NaCl transparent to cm-1 KCl transparent to cm-1 KBr transparent to 400 cm-1

29 Infrared: Low frequency spectra of window materials
Transmission of different window materials: CsI, CsBr, KBr, NaCl, CaF2 and Ge; Thickness: Ge 3 mm, CsBr 4mm, all others 5mm How to prepare samples IR Spectroscopy and how to take an IR spectrum.

30 IR-Absorption by Solvents
Most solvents are of little use for IR spectroscopy because they block most of the of the typical spectral range range ( cm-1). A few notable exceptions are CS2, CHCl3 and CCl4 A complete solution spectrum of a compound can usually be assembled by measuring in CS2 and CHCl3.

31 CCl4

32 http://fy. chalmers. se/OLDUSERS/brodin/MolecularMotions/CCl4modes

33 Vibrations Stretching frequency Bending frequency O H C C—H
Vibrations Stretching frequency Bending frequency C O H Modes of vibration Bending Stretching C—H Wagging 1350 cm-1 Scissoring 1450 cm-1 Symmetrical 2853 cm-1 Rocking 720 cm-1 Asymmetrical 2926 cm-1 Twisting 1250 cm-1

34 Modos vibracionais

35 Vibrations General trends:
Vibrations General trends: Stretching frequencies are higher than bending frequencies (it is easier to bend a bond than stretching or compresing them) Bond involving Hydrogen are higher in freq. than with heavier atoms Triple bond have higher freq than double bond which has higher freq than single bond

36 Symmetrical and asymmetrical stretch
Methyl 2872 cm-1 2962 cm-1 O O 1760 cm-1 1800 cm-1 Anhydride —N H —N H Amino 3300 cm-1 3400 cm-1 —N O —N O Nitro 1350 cm-1 1550 cm-1

37 Estiramentos Ou deformações axiais

38 IR spectra of ALKANES C—H bond “saturated” (sp3) 2850-2960 cm-1
-CH “ and 1375 -CH(CH3) “ and 1370, 1385 -C(CH3) “ and 1370(s), 1395 (m)

39

40 n-pentane 2850-2960 cm-1 CH3CH2CH2CH2CH3 sat’d C-H 3000 cm-1

41 n-hexane CH3CH2CH2CH2CH2CH3

42

43 cyclohexane no 1375 cm-1 no –CH3

44 IR of ALKENES =C—H bond, “unsaturated” vinyl (sp2) 3020-3080 cm-1
RCH=CH & R2C=CH cis-RCH=CHR (v) trans-RCH=CHR C=C bond cm-1 (v)

45 Bond length and strength vs Stretching frequency

46

47

48 1-decene 3020-3080 cm-1 C=C 1640-1680 unsat’d C-H
& RCH=CH2 C=C

49 Alkene In large molecule local symmetry produce weak or absent vibration R trans C=C isomer -> weak in IR C=C R Observable in Raman

50 cis-4-octene 1665

51 trans-4-octene 1665

52 2055 cm-1

53

54

55 Nitrile

56 Other Nitrogen Compounds
Nitriles R-CN : Sharp cm-1 Conjugation moves to lower frequency Isocyanates R-N=C=O Broad ~ 2270 cm-1 Isothiocyanates R-N=C=S 2 Broad peaks ~ 2125 cm-1 Imines / Oximes R 2C=N-R cm-1

57 Como as bandas no IV são afetadas?
Eletronegatividade do carbono (C-H) Números de onda Maiores/ Frequencias maiores 3300 cm-1 3100 cm-1 2900 cm-1

58 styrene no sat’d C-H 1640 C=C & RCH=CH2 mono

59

60

61 Infrared of alcohols and amines
O–H 3400 to 3650 cm1 Usually broad and intense N–H 3300 to 3500 cm1 Sharper and less intense than an O–H

62 Cyclohexanol

63 IR spectra ALCOHOLS & ETHERS
C—O bond (b) cm-1 1o ROH 1050 2o ROH 1100 3o ROH 1150 ethers O—H bond (b) 

64 1-butanol (b) O-H C-O 1o CH3CH2CH2CH2-OH

65 2-butanol O-H C-O 2o

66 tert-butyl alcohol O-H C-O 3o

67 methyl n-propyl ether no O--H C-O ether

68 Free OH and Hydrogen bonded OH

69 Band Shape: OH vs NH2 vs CH

70

71 Infravermelho de aminas

72 Estiramento de compostos carbonílicos

73 Which compound is this? 2-pentanone 1-pentanol 1-bromopentane 2-methylpentane 1-pentanol

74 What is the compound? 1-bromopentane 1-pentanol 2-pentanone 2-methylpentane 2-pentanone

75 Ketone and Conjugation
Conjugation: Lower

76 n Ketone and Ring Strain Factors influencing C=O 2) Ring size
1715 cm-1 1751 cm-1 1775 cm-1 Angle ~ 120o < 120o << 120o n Ring Strain: Higher

77 Factors influencing carbonyl: C=O
3) a substitution effect (Chlorine or other halogens) —C—C— X O n Result in stronger bound  higher frequency 1750 cm-1 4) Hydrogen bonding Decrease C=O strenghtlower frequency 1680 cm-1

78 Factors influencing carbonyl: C=O
5) Heteroatom Inductive effect Resonance effect Weaker bond Lower frequence Stronger bond higher frequency e.g. ester e.g. amides Y C=O Cl Br 1812 inductive OH (monomer) 1760 OR (Ester) NH2 resonance SR

79 n n n Ester Carbonyl Esters C=O ~ 1750 – 1735 cm-1
Conjugation => lower freq. O-C : – or more bands Inductive effect with O reinforce carbonyl => higher n Conjugation with CO weaken carbonyl => Lower n

80 Ester carbonyl: C=O

81 Lactone carbonyl: C=O Lactones  Cyclic Ester 1720 1735 1760 1750 1770
1800

82 Carbonyl compounds : Acids
Carboxylic acid Exist as dimer : Strong Hydrogen bond OH : Very broad  3400 – 2400 cm-1 C=O : broad  1730 – 1700 cm-1 C—O : 1320 – 1210 cm-1 Medium intensity

83 Carbonyl compounds : Acids
OH C=O C=O : cm-1 OH : Very Broad 3300 to 2500 cm-1 C-O : 1285, 1207 cm-1

84 Anhydrides C=O always has 2 bands: 1830-1800 and 1775-1740 cm-1
C—O multiple bands 1300 – 900 cm-1

85 Carbonyl compounds : Aldehydes
~ 1725 cm-1 Conjugation => lower freq. O=C-H : 2 weak bands 2750, 2850 cm-1 C=O : 1724 cm-1

86 Carbonyl compounds : Aldehydes

87 IR SPECTRA: WHAT YOU CAN TELL AT A GLANCE
Is carbonyl group present ( cm-1)? Acid OH: cm-1 Amides N-H: 3400 cm-1 Ester C-O: cm-1 Anhydrides two bands: 1810 and 1760 cm-1 Aldehydes C-H: 2850 and 2750 cm-1 Ketones preceding 5 choices eliminated

88 2) If C=O is absent: ROH OH: cm-1; or ArOH C-O near cm-1 Amines N-H: 3400 cm-1) Ether C-O: cm-1; absence of OH Double bond/aromatic ring: C=C: weak band near 1650 cm-1; cm-1)

89 Triple bonds C=N: 2250 cm-1 (m)
C=C: 2150 cm-1 (w) check for C-H (3300 cm-1) Hydrocarbons 3000 cm-1; 1460 and 1375 cm-1

90 Intensity of C=O vs C=C

91 1758 cm-1

92 1783 cm-1

93 1702 cm-1

94 1715 1686

95 Ligações de hidrogênio
Massa atômica (C-X) Conjugação Ligações de hidrogênio Números de onda menores C-H 3000 C-C 1200 C-O 1100 C-Cl 750 C-Br 600 C-I 500

96 An Amine IR Spectrum => Chapter 12

97 An Amide IR Spectrum => Chapter 12

98 Summary of IR Absorptions