How does the 13 C chemical shift compare to the 1 H chemical shift?

- 13 C chemical shift is approximately 20 times the 1 H chemical shift.

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Learning Goal - NMR

Q: What are the functional groups present in vanillin and lipids, and what does their IR spectrum indicate?

Vanillin : - Functional groups: Hydroxyl (OH), aldehyde (CHO), and methoxy (OCH₃). - IR spectrum: - OH stretch (~3200-3550 cm⁻¹) - CHO stretch (~1690-1740 cm⁻¹), - C-O stretch from methoxy (~1030-1150 cm⁻¹). Lipids : - Functional groups: Ester (COO), aliphatic chains. - IR spectrum: - C=O stretch in ester (~1735-1750 cm⁻¹), - CH₂/CH₃ stretch (~2850-3000 cm⁻¹).

Q: What are the most commonly used IR values in organic chemistry?

Alcohol (O-H): 3200–3400 cm⁻¹ Alkene (C=C): 1600 cm⁻¹ Carbonyl (C=O): 1700 cm⁻¹ C-O bond: 1100 cm⁻¹ Alkyne (C-H): 3300 cm⁻¹ (sharp) N-H: 3500 cm⁻¹ (broad/sharp) Peaks above 3000 cm⁻¹ indicate Alkene C-H, while below indicate Alkane C-H.

Q: What are the key points regarding symmetry in toluene?

Mirror Planes : Toluene has multiple mirror planes. Different Atoms : Two types; carbon and hydrogen. Different Bonds : Mainly C-C and C-H bonds. Chemical Equivalence : Atoms on either side of the mirror plane are equivalent.

Q: What is the effect of rotation on single bonds (sp3)?

Single bonds (sp3) can rotate. Rotation around a bond with hydrogen shows 'no' effect. Rotation with oxygen causes a clear difference.

Q: What does single-bonded carbon rotation result in?

Single-bonded carbon can rotate freely. This rotation allows for various 3D orientations . Carbon’s rotational capability leads to different spatial arrangements.

Q: What type of chemical bonds are unable to rotate?

Double (sp2) and triple (sp) bonds are unable to rotate. Rotation is possible only in single bonds . Example structures show different bonds with arrows indicating non-rotatability.

Q: How many mirror planes does toluene have?

- There is only one mirror plane in toluene.

Q: Describe the different bonds found in toluene.

C-H bonds: 3x (1-a, 3-b, 4-c) C-C bonds: 1x (1-2) C-H Ar bonds: 2x (2-3, 4-5) C-C Ar bonds: 2x (2-3, 3-4)

52 important questions on Learning Goal - NMR

What are the functional groups present in vanillin and lipids, and what does their IR spectrum indicate?

Vanillin:
- Functional groups: Hydroxyl (OH), aldehyde (CHO), and methoxy (OCH₃).
- IR spectrum:
- OH stretch (~3200-3550 cm⁻¹)
- CHO stretch (~1690-1740 cm⁻¹),
- C-O stretch from methoxy (~1030-1150 cm⁻¹).
Lipids:
- Functional groups: Ester (COO), aliphatic chains.
- IR spectrum:
- C=O stretch in ester (~1735-1750 cm⁻¹),
- CH₂/CH₃ stretch (~2850-3000 cm⁻¹).

What are the most commonly used IR values in organic chemistry?

Alcohol (O-H): 3200–3400 cm⁻¹
Alkene (C=C): 1600 cm⁻¹
Carbonyl (C=O): 1700 cm⁻¹
C-O bond: 1100 cm⁻¹
Alkyne (C-H): 3300 cm⁻¹ (sharp)
N-H: 3500 cm⁻¹ (broad/sharp)
Peaks above 3000 cm⁻¹ indicate Alkene C-H, while below indicate Alkane C-H.

How do symmetry and rotation affect the types of C-H and C=C bonds in molecules?

Symmetry and rotation influence molecular bonds.
With high symmetry:
- 1 type of C-C/C=C
- 1 type of C-H
With lower symmetry:
- 5 types of C-C/C=C
- 4 types of C-H

What is the significance of symmetry in benzene in terms of types of carbon and hydrogen atoms?

Benzene has symmetrical structure.
Only one type of C-C/C=C bond exists.
One type of C-H bond is present.
Spectroscopy reveals one signal per equivalent bond or atom.

What are the key points regarding symmetry in toluene?

Mirror Planes: Toluene has multiple mirror planes.
Different Atoms: Two types; carbon and hydrogen.
Different Bonds: Mainly C-C and C-H bonds.
Chemical Equivalence: Atoms on either side of the mirror plane are equivalent.

How many different types of atoms are present in toluene?

5 types of C
5 types of H

What is the effect of rotation on single bonds (sp3)?

Single bonds (sp3) can rotate.
Rotation around a bond with hydrogen shows "no" effect.
Rotation with oxygen causes a clear difference.

What does single-bonded carbon rotation result in?

Single-bonded carbon can rotate freely.
This rotation allows for various 3D orientations.
Carbon’s rotational capability leads to different spatial arrangements.

What type of chemical bonds are unable to rotate?

Double (sp2) and triple (sp) bonds are unable to rotate.
Rotation is possible only in single bonds.
Example structures show different bonds with arrows indicating non-rotatability.

How many mirror planes does toluene have?

- There is only one mirror plane in toluene.

Describe the different bonds found in toluene.

C-H bonds: 3x (1-a, 3-b, 4-c)
C-C bonds: 1x (1-2)
C-H Ar bonds: 2x (2-3, 4-5)
C-C Ar bonds: 2x (2-3, 3-4)

What results from having four different substituents on a carbon?

Four different substituents on a carbon result in:
- Two different mirror images
- An asymmetric carbon centre
- Formation of chirality
- Affects molecular shape, as seen with Thalidomide

How many NMR signals are produced by a molecule with all homotopic protons?

Molecules with all homotopic protons produce 7 or 4 signals.
Homotopic protons are chemically equivalent.

What is the characteristic of molecules with symmetric protons in NMR?

Symmetric protons give 4 signals.
Chemical equivalence results from symmetrical structure.

How do diastereotopic rings affect NMR signals?

Diastereotopic rings result in 7 or 9 signals.
Rings are not chemically equivalent due to different spatial orientations.

What is the NMR signal pattern for diastereotopic alkenes?

Diastereotopic alkenes produce 7 or 6 signals.
Chemical inequivalence due to restricted rotation around the double bond.

How is the response in NMR spectra impacted by the amount of atoms and its use in concentration determination?

Response in NMR spectra relies on the amount of atoms.
Mixture spectra are additive.
Relative peak areas determine concentration.
Equal atom amounts give equal signals, aiding concentration determination.

What is the relation between signal and structure in NMR, and how does it help in structure determination?

NMR links signal to structural info.
Useful for structure determination.
Unique peaks identify chemical groups.
Provides chemical composition info.

How can specific peaks and relaxation times be used in NMR spectroscopy?

Specific peaks identify components.
Relaxation times depend on neighboring atoms.
Lower signals arise for the same atom amount.

What is compared in the charts for NMR and NIR?

Shows signal variation in NMR and NIR.
Uses identical 90 sample Gasoil data-set.
NMR chart displays peaks at higher values.
NIR chart shows signal variation with lower peaks.

What are the differences between NMR and (N)IR spectroscopy according to the slide?

(N)IR relies heavily on chemometrics; NMR uses simpler data processing.
NMR measurements are usually quick ('H-NMR).
High signal variance in NMR relates to chemical changes.
Signal amplitude correlates with nuclei amount.
NMR needs fewer data points for a model.
Solvents required.
NMR is initially more expensive.

What are the basic principles of an atom's magnetic field in NMR?

Atoms possess a small magnetic field.
They have a north and south pole.
A charged nucleus spins, producing the magnetic field B.
Magnetic moments of nuclei are random under normal conditions.
In a magnetic field B₀, nuclear magnetic moments align parallel or anti-parallel.

What happens to atoms in a magnetic field in NMR?

Atoms behave like magnets.
In a magnetic field, poles align with or against the field.
Causes differences in energy levels (excitation).
Used for NMR spectra analysis.

What is the electromagnetic spectrum, and where does NMR fall within it?

The electromagnetic spectrum includes various types of radiation ordered by frequency or wavelength.
Radiation types: γ rays, X rays, UV, NIR, IR, Microwave, Radio waves.
NMR falls within the radio waves section (10^8 to 10^6 Hz).

What happens when a pulse of electromagnetic radiation is applied in a magnetic field?

A pulse of electromagnetic radiation, such as radiowaves, excites particles.
Energy absorption occurs at ΔE.
The system moves from the ground state, \( B_0 \), to the excited state in a magnetic field.

How does \( ^1H \)-NMR work?

Types of H: Intensity and number of signals.
- Symmetry and rotation.
Splitting (s,d,t,q,m):
- Number of neighbors, n+1 rule.
- Hat-trick.
J-coupling (optional):
- Which neighbors are involved?
Shifts: Downfield and upfield.
- Location of peak.
- Dependent on neighboring electrons.

What is a challenge with solvent residual peaks in ¹H-NMR?

Solvent residual peaks are inevitable.
Achieving 100% deuterium is practically impossible.
Chemical shifts depend on the solvent.
Deuterium oxide (D₂O) can exchange with alcohols, amines, and acids.
Check sources for tables with common solvent peaks.

What is the next step in NMR and the main challenge with using this method for carbon?

Next Step in NMR: ¹³C-NMR
Significance: Best percent for structure determination.
Biggest Problem: Low natural abundance of Carbon-13 (1.1%).

What does Carbon NMR detect and what is its natural abundance?

Detects ¹³C, which has approximately 1% natural abundance.
¹³C NMR is decoupled and peaks appear as singlets.

How does the ¹³C chemical shift compare to the ¹H chemical shift?

- ¹³C chemical shift is approximately 20 times the ¹H chemical shift.

Are peak areas in ¹³C-NMR an exact ratio of the number of equivalent carbons?

- Peak areas are not an exact ratio of equivalent carbons.

Does water affect ¹³C-NMR readings?

- Water does not affect the measurements.

What can APT and DEPT differentiate between?

- Can differentiate between C, CH, CH₂, and CH₃ signals.

What are some NMR nuclei other than 1H and 13C?

Different nuclei give spectra with different shifts.
Fluorine, nitrogen, and phosphorus can be used.
These nuclei are outside the scope of these lectures.
Same NMR rules apply universally.

What factors determine the types of carbon in \(^{13}\)C-NMR?

Types of C: Determined by symmetry and rotation.
Hydrogens: Number attached to carbon.
Shifts: Affected by neighboring electrons, influencing peak position.

What is illustrated in the 13C-NMR spectrum of ethylbenzene in CDCl3?

CDC13 Solvent Signal: Appears at 77.16 ppm.
CH3 Group: Appears at 28.9 ppm.
Quaternary Carbon Signals: Around 28.8-28.7 ppm; weaker and narrower.
Aromatic Carbons: 144.3, 144.2, 144.1 ppm.

What are the typical 13C-NMR shifts for different functional groups?

Aldehyde: 190-200 ppm
Ketone: 180-190 ppm
Ester: 160-180 ppm
Aromatic: 120-150 ppm
Alkene: 110-140 ppm
Alkyne: 70-90 ppm
sp3 C-H: 0-50 ppm

What is the carbon chemical shift range for aromatic carbons in 13C-NMR?

- Aromatic: Carbons typically show a shift in the range of 120-150 ppm.

What is shown on the 13C-NMR spectrum of ethylbenzene?

Ethylbenzene peaks:
- Aromatic C: 120-150 ppm
- sp3 C (CH3-): 0-50 ppm
- sp3 C (CH2-): 0-50 ppm

What are the key concepts in ¹³C-NMR related to H-NMR?

Types of C:
- Intensity and number of signals depend on symmetry and number of attached hydrogens.
Splitting:
- Terms like s, d, t, q, m are used.
Shifts:
- Downfield and upfield shifts relate to peak position and neighbors' electrons.

What does the \(^{13}\text{C-NMR}\) spectrum of the given compound indicate?

Chemical Shifts:
- \( \text{C} \): 190-200 ppm
- \( \text{CH(2) and CH(2)} \): 120-140 ppm
- \( \text{CH} \): 40-60 ppm
- \( \text{CH}_3 \): 10-30 ppm
Multiplicity:
- Peak splitting shows coupling with \( \text{CH}_3/\text{CH} \) and \( \text{CH}_2/\text{C} \).

How was 1H-NMR used to analyze instant coffee samples?

98 instant spray-dried coffees dissolved in D₂O.
Principal components analysis (PCA) with linear discriminant analysis (LDA).
Correctly identified 99% of samples to manufacturer.
Blind PCA test with 36 samples: 100% success.

What are the basics of \( ^1H \)-NMR?

Types of H:
- Intensity and number of signals
- Symmetry and rotation
Splitting:
- Patterns: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet)
- Number of neighbors, \( n+1 \) rule
- Hat-trick
J-coupling:
- Optional, considers neighbor interactions

What information does ¹H-NMR spectroscopy provide?

Gives details about all ¹H-containing compounds.
Reveals variations in chemical composition.
Shows signal split or broadness, indicating neighboring nuclei.
Assists in structure determination with peak positions and splitting.

What is a key disadvantage of using ¹H-NMR spectroscopy?

Water presence is problematic.
Requires solvents without ¹H.

How is ¹H NMR useful in structure determination?

Peak positions depend on neighboring groups.
Peak splitting depends on neighboring hydrogen protons.
Provides a quick analysis of structural details.

What is ¹H-NMR used for in structure determination?

¹H-NMR is the most used NMR technique.
It's known as the "bread and butter" for structure determination.
Participants were asked about their usage and experience with ¹H-NMR.

What are the basics of ^1H-NMR as illustrated with ethylbenzene?

^1H-NMR analyzes hydrogen types.
Signal intensity and number depend on H types.
Symmetry and rotation affect signals.
Ethylbenzene serves as an example.

What does the splitting pattern in a \( ^1H \)-NMR spectrum indicate for the compound shown?

Splitting: Interaction with neighboring nuclei, showing distinct split peaks.
Protons labeled as:
- \( H_a \): Doublet
- \( H_b \): Triplet
- \( H_c, H_d, H_e \): Complex splitting

What are the \( ^1H \)-NMR splitting patterns shown?

Pattern 1:
- \(\delta\) 1.37 - Singlet
- \(\delta\) 0.85 - Multiplet
- Highlighted protons: \(\mathrm{H}\)
Pattern 2:
- \(\delta\) 1.51 - Doublet
- \(\delta\) 3.50 - Triplet
- Highlighted protons: \(\mathrm{H}\)

What are some trends in \( ^1H \)-NMR shifts?

Downfield shift: \( \text{CH} > \text{CH}_2 > \text{CH}_3 \)
Chemical shift values:
- \( \text{H-C=CH}_2 \): around 5-6 ppm
- \( \text{RCH}_2\text{R} \): around 1-2 ppm
- \( \text{R}_3\text{CH} \): near 1 ppm
\( \text{OH or NH} \) shows variable shifts
Referenced with TMS (0 ppm)

What are the chemical shift ranges in ¹H-NMR for different functional groups?

Aromatics: 6.0 - 8.5 ppm
Alcohols: 3.2 - 5.5 ppm
Ethers/Sulfides: 2.8 - 4.5 ppm
Saturated alkanes: 0.8 - 1.5 ppm
Alkenes: 4.5 - 6.5 ppm
Esters: 3.7 - 4.1 ppm
Amides: 5.0 - 8.5 ppm
Aldehydes: 9.5 - 10.5 ppm

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