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

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Apresentação em tema: "QFL-4030 Métodos espectroscópicos de análise (2014) Home Page: (courses)"— Transcrição da apresentação:

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

2 Literatura Silverstein, R. M., Webster, F. X. and Kiemle, D. J. (2005) Spectrometric identification of organic compounds, 7 th 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: https://www.youtube.com/watch?v=DDTIJgIh86E

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 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, Papaverina: Merck, Cocaína: Wöhler, Escopolamina: Landenburg, Efedrina: Nagai, Tubocurarina: Boehm, Insulina: Abel, 1929.

6 Penicilina: Fleming, Dicumarol: Link, Cloranfenicol: Burkholder, Reserpina: Müller, Prostaglandinas: Bergströn, 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 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. 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. Quinine (natural antimalarial compound) Cinchona officinalis (quinine bark - Rubiaceae) Synthetic derivatives:

11 Como diferenciar uma molécula de outra? 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 Ponto de fusão, índice de refração, forma, tamanho, etc…

12 Análise elementar – Determinação fórmula mínima C x H y O z + O 2 (excesso) = x CO 2 + y/2 H 2 O 9.83 mg mg 9.52 mg C x H y O z, x = 64.6%; y = 10.8%; z = 24.6% C 7 H 14 O 2 Fórmula mínima

13 Eletronic transitions Bond breaking Nuclear spin transitions Vibrational transitions EMUV-VISIVRMN frequency energy

14 A9tico.png/700px-Espectro_Eletromagn%C3%A9tico.png Comparação do comprimento de onda

15 General scheme for structural elucidation of natural compounds

16 C-O OH MM = 70 u.a. CH 2 OH CxHyOzC4H6OC4H6O CH 2 CH -18 (OH)  C-H CCCC

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

18

19 Infrared radiation λ = 2.5 to 17 μm (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 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 => (cm -1 ) => proportional to energy Depends on: Relative masses of atoms Force constant of bonds Geometry of atoms  Older system uses the wavelenght  (  m => m) cm -1 = 10 4 /  m

21 Lei de Hooke

22

23 Instrumentação

24 IR source  sample  prism  detector graph of % transmission vs. frequency => IR spectrum v (cm -1 ) 100 %T 0

25 Intensity: T%T Transmittance (T) or %T T T = I I0I0 A Absorbance (A) A A = log I I0I0 Intensity in IR IR%IRtransmittance IR : Plot of %IR that passes through a sample (transmittance) Wavelenght 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 Sampling => plates, polished windows, Films … Must be transparent in IR NaCl, KCl : Cheap, easy to polish NaCl cm -1 NaCl transparent to cm -1 KCl cm -1 KCl transparent to cm -1 KBr 400 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, CaF 2 and Ge; Thickness: Ge 3 mm, CsBr 4mm, all others 5mm How to prepare samples IR Spectroscopy and how to take an IR spectrum. https://www.youtube.com/watch?v=FfI5BczOXQ8

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 CS 2, CHCl 3 and CCl 4 A complete solution spectrum of a compound can usually be assembled by measuring in CS 2 and CHCl 3.

31 CCl 4

32

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

34 Modos vibracionais /Vibrational_Modes

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

36 Symmetrical and asymmetrical stretch Methyl 2872 cm -1 Symmetrical Stretch Asymmetrical Stretch —C—H—C—H—C—H—C—HHH —C—H—C—H—C—H—C—HHH Anhydride OOO 1760 cm cm cm -1 OOOAmino Nitro —N—N—N—NHH 3300 cm cm cm cm -1 —N—N—N—NHH —N—N—N—NOO —N—N—N—NOO

37 Estiramentos Ou deformações axiais

38 IR spectra of ALKANES C—H bond “saturated” (sp 3 ) cm cm -1 -CH CH 3 + “ and CH(CH 3 ) 2 + “ and 1370, C(CH 3 ) 3 + “ and 1370(s), 1395 (m)

39

40 n-pentane CH 3 CH 2 CH 2 CH 2 CH cm &1375 cm cm -1 sat’d C-H

41 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 n-hexane

42

43 cyclohexane no 1375 cm -1 no –CH 3

44 IR of ALKENES =C—H bond, “unsaturated” vinyl (sp 2 ) cm RCH=CH & R 2 C=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 & RCH=CH 2 C=C unsat’d C-H cm -1

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

50 1665 cis-4-octene

51 1665 trans-4-octene

52 2055 cm-1

53

54

55 Nitrile

56 Other Nitrogen Compounds Nitriles Isocyanates Isothiocyanates Imines / Oximes R-C  N : Sharp 2250 cm -1 Conjugation moves to lower frequency R-N=C=O Broad ~ 2270 cm -1 R-N=C=S 2 Broad peaks ~ 2125 cm -1 R 2 C=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 cm cm -1

58 styrene no sat’d C-H & RCH=CH 2 mono 1640 C=C

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 1 o ROH o ROH o ROH1150 ethers O—H bond (b) 

64 1-butanol CH 3 CH 2 CH 2 CH 2 -OH C-O 1 o (b) O-H

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

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

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? a)2-pentanone b)1-pentanol c)1-bromopentane d)2-methylpentane 1-pentanol

74 What is the compound? a)1-bromopentane b)1-pentanol c)2-pentanone d)2-methylpentane 2-pentanone

75 Ketone and Conjugation Conjugation: Lower

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

77 Factors influencing carbonyl: C=O 3)  substitution effect (Chlorine or other halogens) —C—C——C—C——C—C——C—C— XO 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 Stronger bond higher frequency e.g. ester Resonance effect Weaker bond Lower frequence e.g. amides Y C=O Cl Br OH (monomer) OR (Ester) NH2 SR inductive resonance

79 Ester Carbonyl EstersC=O ~ 1750 – 1735 cm -1 O-C : 1300 – or more bands Conjugation => lower freq. Inductive effect with O higher Inductive effect with O reinforce carbonyl => higher Conjugation with CO Lower Conjugation with CO weaken carbonyl => Lower

80 Ester carbonyl: C=O

81 Lactone carbonyl: C=O Lactones  Cyclic Ester

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 C=O OH C=O : 1711 cm -1 OH : Very Broad 3300 to 2500 cm -1 C-O : 1285, 1207 cm -1

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

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

86 Carbonyl compounds : Aldehydes

87 IR SPECTRA: WHAT YOU CAN TELL AT A GLANCE 1)Is carbonyl group present ( cm -1 )? Acid OH: cm -1 Amides N-H: 3400 cm -1 Ester C-O: cm -1 Anhydridestwo bands: 1810 and 1760 cm -1 AldehydesC-H: 2850 and 2750 cm -1 Ketonespreceding 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 bondsC=N: 2250 cm -1 (m) C=C: 2150 cm-1 (w) check for C-H (3300 cm -1 ) Hydrocarbons3000 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

95 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 Chapter 1296 An Amine IR Spectrum =>

97 Chapter 1297 An Amide IR Spectrum =>

98 Summary of IR Absorptions


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