QFL-4030 Métodos espectroscópicos de análise (2014)

Home Page: http://www2.iq.usp.br/docente/majokato (courses)

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 CollegesRoyal Society of Chemistry – Advancing the Chemical Sciences:https://www.youtube.com/watch?v=DDTIJgIh86E

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.

Programa

Espectroscopia no UV-vis,

infravermelho (IV),

espectrometria de massas e

ressonância magnética nuclear.

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.

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

quinina

N

NHO

MeO

Uso como antimalárico: Desde 1638

Isolamento: 1820 por Pelletier e Caventou

Síntese: 1944 por Woodward

Determinação estrutural da quinina porreações de degradação

quiteninaquinina

KMnO4

N

N

CO2H

HO

MeO

N

NHO

MeO

meroquinenoácido

quinínico

+NO

OHCrO3 N

CO2HMeO

N

NMeO

O

ac. cincoloipônico

N

CO2H

HO2C

NOOH

meroquineno

N

CNCH(CO2Et)2

N

CN

-cloropropionacetal

-cloropropional

ClCH2CH2CHO

NH3

CH(OEt)2

ClCl

CH(OEt)2

Confirmadas por síntese dos fragmentos obtidos

N

NHH2N

CH3OPrimaquineIs 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.

N

NHO

CF3

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.

N

MeO

HO NQuinine (natural antimalarial compound)

Cinchona officinalis (quinine bark - Rubiaceae)

Synthetic derivatives:

Como diferenciar uma molécula de outra?

N

NHO

CF3

HO

H

• 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…

Análise elementar – Determinação fórmula mínima

CxHyOz + O2 (excesso) = x CO2 + y/2 H2O

9.83 mg 23.26 mg 9.52 mg

CxHyOz, x = 64.6%; y = 10.8%; z = 24.6% C7H14O2

Fórmula mínima

Eletronictransitions

Bond breaking

Nuclear spintransitions

Vibrationaltransitions

EM UV-VIS IV RMN

frequency

energy

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Espectro_Eletromagn%C3%A9tico.png/700px-Espectro_Eletromagn%C3%A9tico.png

Comparação do comprimento de onda

Plant tissue,microorganism

and etc

Extraction bystem distillation,organic solvent

or CO2

Fractionation and purification

(solvent extractions,column chromatography,

HSCC, etc)

Purecompound

Determination ofmolecular formula

(elemental analysisor HRMS)

Determination offunctional groups

(IR, UV, 1H and 13C NMR)

Determination of types of carbons(CH3, CH2, CH, C)and sub-structures

(1H NMR: multiplicities and integration; 13C NMR: chemical shifts and DEPT 135)

Determination ofconnectivities and planar

structures (J3 1H-1H;13C NMR: HSQC; HMBC)

Determination oftridimensional structuresor spatial relationships

(J3 1H-1H;13C NMR: NOESY, TOCSY)

Determination ofabsolute configuration

(optical rotation, circular dichroisms and R-X)

Chromatographicprofile, melting point,

boiling point, refraction index, etc)

General scheme for structural elucidation of natural compounds

𝐼=𝐶−𝐻2−𝑋2+𝑁2+1=2

C-O

OH

MM = 70 u.a.

CH2 OH

CxHyOz C4H6O

CH2 CH

-18 (OH)

C-H

C-HCC

HC C CH2 CH2 OH

Análise funcional orgânica

Espectrofotometria no Ultravioleta e

infravermelho

Determinação de grupos funcionais:

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

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 => n (cm-1) => proportional to energy

n Depends on:

• Relative masses of atoms• Force constant of bonds• Geometry of atoms

Older system uses the wavelenght l (mm => 10-6 m)

cm-1 = 104 / mm

Lei de Hooke

Instrumentação

IR source è sample è prism è detector

graph of % transmission vs. frequency

=> IR spectrum

4000 3000 2000 1500 1000 500

v (cm-1)

100

%T

0

Intensity: Transmittance (T) or %T

T =II0

Absorbance (A)

A = log II0

Intensity in IR

IR : Plot of %IR that passes through a sample (transmittance) vs Wavelenght

Instrumentação

Espectro no IV

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 4000 - 650 cm-1

KCl transparent to 4000 - 500 cm-1

KBr transparent to 400 cm-1

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.

https://www.youtube.com/watch?v=FfI5BczOXQ8

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 (4000 - 600 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.

CCl4

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

Vibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm

Modes of vibration

C—HStretchingBending C

OH

H

H

Symmetrical 2853 cm-1

H

H

Asymmetrical 2926 cm-1

H

H

H

H

Scissoring1450 cm-1

Rocking720 cm-1

HH

HH

Wagging1350 cm-1

Twisting1250 cm-1

Stretchingfrequency

Bendingfrequency

Modos vibracionais

http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes

Vibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm

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

Symmetrical and asymmetrical stretch

Methyl 2872 cm-1

Symmetrical Stretch Asymmetrical Stretch

—C—H

H

H

—C—HH

H

Anhydride

O

O O1760 cm-1

2962 cm-1

1800 cm-1

O

O O

Amino

Nitro

—NH

H3300 cm-1 3400 cm-1

1350 cm-1 1550 cm-1

—NH

H

—N

O

O—N

O

O

EstiramentosOu deformações axiais

IR spectra of ALKANESC—H bond “saturated”

(sp3) 2850-2960 cm-1

+ 1350-1470 cm-1

-CH2- + 1430-1470

-CH3 + “ and 1375

-CH(CH3)2 + “ and 1370, 1385

-C(CH3)3 + “ and 1370(s), 1395 (m)

n-pentane

CH3CH2CH2CH2CH3

3000 cm-1

1470 &1375 cm-1

2850-2960 cm-1

sat’d C-H

CH3CH2CH2CH2CH2CH3

n-hexane

cyclohexane

no 1375 cm-1

no –CH3

IR of ALKENES=C—H bond, “unsaturated” vinyl

(sp2) 3020-3080 cm-1

+ 675-1000

RCH=CH2 + 910-920 & 990-1000

R2C=CH2 + 880-900

cis-RCH=CHR + 675-730 (v)

trans-RCH=CHR + 965-975

C=C bond 1640-1680 cm-1 (v)

Bond length and strength vs

Stretching frequency

Bond C-H =C-H -C-H

Length 1.08 1.10 1.12

Strenght 506 kJ 444 kJ 422 kJ

IR freq. 3300 cm-1 3100 cm-1 2900 cm-1

1-decene

910-920 & 990-1000 RCH=CH2

C=C 1640-1680

unsat’dC-H

3020-3080 cm-1

Alkene

In large molecule local symmetry produce weak or absent vibration

C=C

R

Rtrans C=C isomer -> weak in IR

Observable in Raman

1665

cis-4-octene

1665

trans-4-octene

2055 cm-1

Nitrile

Other Nitrogen Compounds

Nitriles

Isocyanates

Isothiocyanates

Imines / Oximes

R-CN : 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 2C=N-R 1690 - 1640 cm-1

Como as bandas no IV são afetadas?

Eletronegatividade do carbono (C-H)Números de onda

Maiores/Frequencias maiores

C C H C C H C C H

3300 cm-1 3100 cm-1 2900 cm-1

styrene

no sat’d C-H

910-920 & 990-1000

RCH=CH2mono

1640C=C

Infrared of alcohols and amines• O–H 3400 to 3650 cm1

– Usually broad and intense• N–H 3300 to 3500 cm1

– Sharper and less intense than an O–H

Cyclohexanol

IR spectra ALCOHOLS & ETHERS

C—O bond 1050-1275 (b) cm-1

1o ROH 1050

2o ROH 1100

3o ROH 1150

ethers 1060-1150

O—H bond 3200-3640 (b)

1-butanol

CH3CH2CH2CH2-OH

C-O 1o

3200-3640 (b) O-H

2-butanol

C-O 2o

O-H

tert-butyl alcohol

C-O 3oO-H

methyl n-propyl ether

no O--H

C-O ether

Free OH and Hydrogen bonded OH

Band Shape: OH vs NH2 vs CH

Infravermelho de aminas

O

H

O

R

O

OR

O

OH

O

NH2

C C C

C C

1740-1690 cm-1 1750-1680 cm-1 1750-1735 cm-1

1780-1710 cm-1 1690-1630 cm-1

Estiramento de compostos carbonílicos

Which compound is this?a) 2-pentanoneb) 1-pentanolc) 1-bromopentaned) 2-methylpentane

1-pentanol

What is the compound?a) 1-bromopentaneb) 1-pentanolc) 2-pentanoned) 2-methylpentane

2-pentanone

Ketone and ConjugationnConjugation: Lower

Ketone and Ring Strain

nRing Strain: Higher

Factors influencing C=O

2) Ring size

O

1715 cm-1

Angle ~ 120o

CH3

CH3

O

O

1751 cm-1

< 120o

O

1775 cm-1

<< 120o

Factors influencing carbonyl: C=O 3) a substitution effect (Chlorine or other halogens)

—C—C—

X

O

Result in stronger bound higher frequency n

O

Cl 1750 cm-1

4) Hydrogen bonding Decrease C=O strenghtlower frequency

O

OCH3

OH

1680 cm-1

Factors influencing carbonyl: C=O

5) Heteroatom

Y

R

O

Inductive effectStronger bond

higher frequency

e.g. ester

Y

R

O

Resonance effectWeaker bondLower frequence

e.g. amides

Y C=O

ClBrOH (monomer)OR (Ester)

1815-17851812

17601705-1735

NH2

SR1695-1650

1720-1690

inductive

resonance

Ester Carbonyl

Esters C=O n ~ 1750 – 1735 cm-1

O-C : 1300 – 1000 2 or more bands

Conjugation => lower freq.

R OR

O

Inductive effect with O reinforce carbonyl => higher n

Conjugation with CO weaken carbonyl => Lower n

Ester carbonyl: C=O

Lactone carbonyl: C=O

Lactones Cyclic Ester

O

O

17351720 1760

17701750 1800

O

O

O

O

OO

OO O

O

Carbonyl compounds : Acids

Carboxylic acid

Exist as dimer :

CH3 C

OH

O

CH3C

OH

O

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

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

Anhydrides

CH3 O

O

CH3

OC=O always has 2 bands:

1830-1800 and 1775-1740 cm-1

C—O multiple bands 1300 – 900 cm-1

Carbonyl compounds : AldehydesAldehydes C=O n ~ 1725 cm-1

O=C-H : 2 weak bands 2750, 2850 cm-1

Conjugation => lower freq.

C=O : 1724 cm-1

Carbonyl compounds : Aldehydes

IR SPECTRA: WHAT YOU CAN TELL AT A GLANCE

1) Is carbonyl group present (1820-1650 cm-1)?

Acid OH: 3400-2400 cm-1

Amides N-H: 3400 cm-1

Ester C-O: 1300-1000 cm-1

Anhydrides two bands: 1810 and 1760 cm-1

Aldehydes C-H: 2850 and 2750 cm-1

Ketones preceding 5 choices eliminated

2) If C=O is absent:

ROH OH: 3400-3300 cm-1;

or ArOH C-O near 1300-1000 cm-1

Amines N-H: 3400 cm-1)

Ether C-O: 1300-1000 cm-1; absence of OH

Double bond/aromatic ring:

C=C: weak band near 1650 cm-1;

1600-1450cm-1)

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

Intensity of C=O vs C=C

1758 cm-1

1783 cm-1

1702 cm-1

1686

1715

Massa atômica (C-X)Conjugação

Ligações de hidrogênio

Números de ondamenores

C-H3000

C-C1200

C-O1100

C-Cl750

C-Br600

C-I500

Chapter 12 96

An Amine IR Spectrum

=>

Chapter 12 97

An Amide IR Spectrum

=>

Summary of IR Absorptions