ib chemistry on nuclear magnetic resonance, chemical shift and splitting pattern
TRANSCRIPT
Classical method
Analytical Techniques
Classical method
Qualitative analysis
Quatitative analysis
Chemical test
Flame test
Titration
Gravimetric
Instrumental method
Spectroscopy analysis
Separation analysis
Nuclear Magnetic Resonance Spectroscopy
Atomic Absorption/Emission Spectroscopy
InfraRed /UV Spectroscopy
Mass Spectroscopy
High Performance Liquid Chromatography
Gas Liquid Chromatography
Paper/Thin Layer/Column Chromatography
Analytical Techniques
Quatitative analysis Qualitative analysis Separation analysis
Flame test Chemical test
Melting/boiling point
Gravimetric Titration Distillation Precipitation
Study on Identification, Structural Determination, Quantification and Separation
Involve Qualitative and Quantitative analysis • Quantitative – Amt present in sample/mix • Qualitative – Identity species present in impure sample • Structural – Determination of structure of molecule • Separation of mix – Chromatographic Techniques • Identification of functional gps • Purity of substances
• Spectroscopy measures interaction of molecules with electromagnetic radiation • Particles (molecule, ion, atom) can interact/absorb a quantum of light
Spectroscopy
Electromagnetic Radiation
Nuclear spin
High Energy Radiation
Gamma/X ray
Transition of inner electrons
UV or visible
Transition of outer most valence electrons
Infrared
Molecular vibration
Microwave
Molecular rotation
Radiowaves
Low Energy Radiation
Infra Red Spectroscopy Nuclear Magnetic Resonance Spectroscopy
Ultra Violet Spectroscopy
Atomic Absorption Spectroscopy
Velocity of light (c ) = frequency (f) x wavelength (λ) - c = f λ • All electromagnetic waves travel at speed of light (3.00 x 108ms-1) • Radiation with high ↑ frequency – short ↓ wavelength • Electromagnetic radiation/photon carry a quantum of energy given by
E = hf
hcE
h = plank constant = 6.626 x 10-34 Js f = frequency λ = wavelength
Click here notes spectroscopy
Electromagnetic Radiation and Spectroscopy
Radiowaves
Nuclear spin
Nuclear Magnetic Resonance Spectroscopy
• Organic structure determination • MRI and body scanning
Infrared
Molecular vibration
Infrared Spectroscopy
UV or visible
Transition of outer valence electron
• Organic structure determination • Functional gp determination • Measure bond strength • Measure degree unsaturation in fat • Measure level of alcohol in breath
Electromagnetic Radiation
UV Spectroscopy Atomic A Spectroscopy
• Quantification of metal ions • Detection of metal in various samples
Electromagnetic Radiation Interact with Matter (Atoms, Molecules) = Spectroscopy
Nuclear Magnetic Resonance Spectroscopy (NMR) • Involve nucleus (proton + neutron) NOT electron • Proton + neutrons = Nucleons • Nucleons like electrons have spin and magnetic moment (acts like tiny magnet)
Nuclei with even number of nucleon (12C and 16O) • Even number of proton and neutron – NO net spin • Nucleon spin cancel out each other –Nucleus have NO overall magnetic moment – NOT absorb radiowave
Nuclei with odd number of nucleon (1H, 13C, 19F, 31P) -Nucleon have net spin – Nucleus have NET magnetic moment – Absorb radiowave
• Nuclei with net spin – magnetic moment will interact with radiowaves • Nuclei have a “spin” associated with them (i.e., they act as if they were spinning about an axis) due to the spin associated with their protons and neutrons. • Nuclei are positively charged, their spin induces a magnetic field
• NMR spectroscopy does not work for nuclei with even number of protons and neutrons - nuclei have no net spin.
Nuclear Magnetic Resonance Spectroscopy (NMR)
Spin cancel each other
Net spin
Main features of HNMR Spectra 1. Number of diff absorption peaks – Number of diff proton/chemical environment 2. Area under peaks - Number of hydrogen in a particular proton/chemical environment (Integration trace) - Ratio of number of hydrogen in each environment 3. Chemical shift - Chemical environment where proton is in - Spinning electrons create own magnetic field, creating a shielding effect - Proton which are shielded appear upfield. (Lower frequency for resonance to occur) - Proton which are deshielded appear downfield. (Higher frequency for resonance to occur) - Measured in ppm (δ) 4. Splitting pattern - Due to spin-spin coupling - Number of peak split is equal to number of hydrogen on neighbouring carbon +1 (n+1) peak
Chemical Shift NMR spectrum CH3CH2Br
Number of peaks
Area under peaks Chemical shift
Splitting pattern
Nuclear Magnetic Resonance Spectroscopy (NMR)
Click here khan NMR videos.
Absence of External magnetic Field (EMF) • TWO nuclear spin have same energy level.
• External MF applied to atomic nuclei, MF of nuclei align themselves either with or against MF • Nuclei have a slight preference for parallel alignment with the applied field as it has a slightly lower energy • Nuclei can absorb energy to move/flip to higher energy level by absorbing energy in radio freq region
Presence of External Magnetic Field (EMF) • TWO nuclear spin split to TWO diff energy level
Presence of External Magnetic Field (EMF)
Absence of EMF • Two spins in same energy level
Presence of EMF • Two spins in diff energy level • Lower spin nuclei absorb radio freq equivalent to ∆E • Move to higher energy level
Lower spin nuclei align with magnetic field
High spin nuclei align against magnetic field
∆E
Nuclear Magnetic Resonance Spectroscopy (NMR)
H ׀ H – C – H
H ׀ H – C
Proton in nucleus – have spin – generate its magnetic field (MF) Electron around nucleus – have spin- also generate its MF Proton shielded by MF produced by electron - appear UPFIELD Proton deshielded by electron withdrawing gp - appear DOWNFIELD
Chemical Shift (Shielding Effect)
Presence of EMF • Two spins in diff energy level • Lower spin nuclei absorb radio freq equivalent to ∆E • Move to higher energy level
∆E
∆E is smaller
Without SHIELDING EFFECT • Energy of ∆E absorb by H to move to higher energy level
Upfield Downfield
SHIELDING EFFECT • Electron around H produce MF and shield the H • H in CH3 will experience less EMF (SHIELDED) • Absorb at lower radiofreq to move to higher level • ∆E absorb by H to move to higher energy level is less • Appear upfield.
Absence of EMF • Two spins in same energy level
Absence of EMF • Two spins in same energy level
Presence of EMF • Two spins at diff energy level
Presence of EMF • Two spins at diff energy level
MF
N
S
H nucleus proton
H nucleus shield by electron MF
proton MF
N
S
- H
H ׀ H – C – H
∆E
∆E is higher
DESHIELDING EFFECT • Electron withdrawn by C=O gp • Carbonyl gp has electron withdrawing effect • Less electron around H in CH3
• H in CH3 deshielded, experience greater EMF • ∆E absorb by H, to move to high energy is higher • Absorb at higher radiofreq, to move to high level • Appear downfield
Chemical Shift (Deshielding Effect)
Downfield Upfield
Presence of EMF • Two spins in diff energy level • Lower spin nuclei absorb radio freq equivalent to ∆E • Move to higher energy level
Absence of EMF • Two spins in same energy level
proton H nucleus
Presence of EMF • Two spins at diff energy level
Without SHIELDING EFFECT • Energy of ∆E absorb by H to move to higher energy level
S
N
MF
H nucleus deshield by elec MF
proton
Absence of EMF • Two spins in same energy level Presence of EMF
• Two spins at diff energy level
N
S
MF
Proton in nucleus – have spin – generate its magnetic field (MF) Electron around nucleus – have spin- also generate its MF Proton shielded by MF produced by electron - appear UPFIELD Proton deshielded by electron withdrawing gp - appear DOWNFIELD
H ׀ H – C – H
No shielding
∆E
∆E is smaller
Without any SHIELDING EFFECT • Energy of ∆E absorb by H to move to higher energy level
SHIELDING EFFECT • Electron around H produce MF and shield H • H in CH3 experience less EMF (SHIELDED) •∆E absorb by H to move to higher energy level is less • Appear upfield.
Chemical Shift (Shielding and Deshielding Effect)
∆E is higher
Absence of EMF • Two spins in same energy level
Presence of EMF • Two spins at diff energy level
Shielding Effect
H nucleus proton
MF
S
N
H nucleus deshield by elec MF
proton
DESHIELDING EFFECT • Electron withdrawn by C=O gp • Carbonyl gp has electron withdrawing effect • Less electron around H in CH3
• H in CH3 deshielded, experience greater EMF • ∆E absorb by H, to move to high energy is higher • Absorb at higher radiofreq, to move to high level • Appear downfield
H nucleus shield by elec MF
proton N
S
N
S
Deshielding Effect
MF
MF
Chemical Shift (Shielding and Deshielding Effect)
Shielding/Deshielding: • Electron circulate nucleus, create MF opposing external MF. • Each nucleus experience a slightly diff magnetic field • (Sum external field and field from electron cloud). • Energy a nucleus achieve resonance depend on its surrounding. • Freq absorption depend on electron density around nucleus
Chemical shift of various electron withdrawing gp
- Electron withdrawn from CH3 by C=O • Deshield H in CH3 • Absorb at slightly higher freq • Upfield ≈ 2.1
• Electron withdrawn from CH2 by COO • Stronger electron withdrawing effect • Higher ↑ Deshielding effect on H in CH2 • Absorb at Higher ↑ freq • Slightly Downfield ≈ 4.1
• Electron withdrawn by benzene • Stronger electron withdrawing effect • Higher ↑ deshielding effect on H • Absorb at Very high ↑ freq • Very Downfield ≈ 7.3 - 8
• Electron withdrawn from H by CHO • Very strong electron withdrawing effect • Higher ↑ Deshielding effect on H in CHO • Absorb at Very High ↑ freq • Very Very Downfield ≈ 9.7
• Electron withdrawn by COOH • Very strong electron withdrawing effect • Highest deshielding effect on H • Absorb at Very High ↑ freq • Very Very Very Downfield ≈ 12
Upfield
9.7
Downfield
12
Tetramethyl Silane (TMS) as STD •Strong peak upfield (shielded) •Silicon has lower EN value < carbon • Electron shift to carbon • H in CH3 more shielded • Experience lower EMF, absorb ↓ freq • UPFIELD ≈ 0
Click here for more complicated proton chemical shift
• 3 diff proton environment • Ratio of 3:2:1
CH3
• chemical shift ≈ 1 • integration = 3 H • split into 3
CH2
• chemical shift ≈ 3.8 • integration = 2 H • split into 4
OH
• chemical shift ≈ 4.8 • integration = 1 H • No split (Singlet)
3 2 1
Upfield
12
Advantages using TMS • Volatile and can be removed from sample • All 12 hydrogen in same proton environment • Single strong peak, upfield, wont interfere with other peak • All chemical shift, in ppm (δ) are relative to this STD, ( zero)
Nuclear Magnetic Resonance Spectroscopy (HNMR)
HO-CH2-CH3
CH3
׀ H3C – Si – CH3
׀ CH3
Click here Spectra database (Ohio State) Click here Spectra database (NIST)
TMS
Downfield
1H NMR Spectrum
O ‖
HO-C-CH2-CH3
3 diff proton environment, Ratio H - 3:2:3 • Peak A – split to 3 (2H on neighbour C) • Peak B - No split • Peak C – split to 4 (3H on neighbour C)
3 diff proton environment, Ratio H - 3:2:1 • Peak A – split to 3 (2H on neighbour C) • Peak B – split to 4 (3H on neighbour C) • Peak C – No split
A B
C
B
A
C
12
3 2 3
3 2 1
O ‖ CH3-C-O-CH2-CH3
O ‖ CH3-C-CH2-CH2-CH3
3 diff proton environment, Ratio H - 3:2:1 • Peak A – split to 3 (2H on neighbour C) • Peak B – split to 4 (3H on neighbour C) • Peak C – No split
4 diff proton environment, Ratio H - 3:2:2:3 • Peak A – split to 3 (2H on neighbour C) • Peak B – split to 6 (5H on neighbour C) • Peak C – No split • Peak D – split to 3 (2H on neighbour C)
A
B C
3
B
A C
D
2 1
3 2 2 3
HO-CH2-CH3
1H NMR Spectrum
O ‖ H-C-CH3
4 diff proton environment, Ratio H – 3:2:2:3 • Peak A – split to 3 (2H on neighbour C) • Peak B – split to 6 (5H on neighbour C) • Peak C – No split • Peak D – split to 3 (2H on neighbour C)
A B C D
2 diff proton environment, Ratio H - 3:1 • Peak A – split to 2 (1H on neighbour C) • Peak B – split to 4 (3H on neighbour C)
9.8
A
B
3 2 2 3
3 1
O ‖ CH3-C-O-CH2-CH2-CH3
1H NMR Spectrum
3 diff proton environment, Ratio H - 6:1:1 • Peak A – split to 2 (1H on neighbour C) • Peak B – No split • Peak C – split to 7 (6H on neighbour C)
O CH3
׀ ‖ CH3-C-O-C-H
׀ CH3
A
B
C
A
B
C
3 diff proton environment, Ratio H - 6:3:1 • Peak A – split to 2 (1H on neighbour C) • Peak B – No split • Peak C – split to 7 (6H on neighbour C)
Molecule with plane of symmetry
6 1 1
6 3 1
CH3
׀ H-C-OH
׀ CH3
Molecule with plane of symmetry
1H NMR Spectrum
2 diff proton environment, Ratio H – 6:4 • Peak A – split to 3 (2H on neighbour C) • Peak B – split to 4 (3H on neighbour C)
A
B
A
B
6 4
9 1
2 diff proton environment, Ratio H – 9:1 • Peak A – No split • Peak B – No split
Molecule with plane of symmetry
O ‖ CH3-CH2-C-CH2-CH3
Molecule with plane of symmetry
O CH3
׀ ‖ H-C-C-CH3
׀ CH3
1H NMR Spectrum
4 diff proton environment, Ratio H - 6:1:1:2 • Peak A – split to 2 (1H on neighbour C) • Peak B – split to 7 (6H on neighbour C) • Peak C – No split • Peak D – split to 2 (1H on neighbour C)
A
B D
C
2 diff proton environment, Ratio H – 6:1 • Peak A – split to 2 (1H on neighbour C) • Peak B – split to 7 (6H on neighbour C)
A
B
6 1 1 2
6 1
Molecule with plane of symmetry
CH3
׀ HO-CH2-CH
׀ CH3
Molecule with plane of symmetry CH3-CH-CH3
׀ CI
1H NMR Spectrum