Spectroscopy

Spectroscopy techniques, specifically IR and NMR, are crucial for determining molecular structures of organic compounds.
- Importance: Organic compounds display vast structural variations, where subtle changes can significantly impact their properties and physiological effects.
- Structural Elucidation: Essential for identifying molecular structures through various methods.

Chemicals and Hormones:
- Dimethyltryptamine (DMT): A hallucinogen.
- Serotonin: A neurotransmitter.
- Estradiol: A female sex hormone.
- Testosterone: A male sex hormone.

Canadian Food Inspection Agency (CFIA) uses IR spectroscopy to ensure food safety and quality.
- Collects a “fingerprint” spectrum unique to each food product.
- Fruit Juice Fraud: Infrared spectroscopy can determine the presence of low-cost additives or substitutes in fruit juices.

Definition: The number of π bonds and/or rings in a molecule, which indicates saturation level.
Calculation:
- Formula: $DOU = rac{(2C + 2) - H + Group ext{ V} - Group ext{ VII}}{2}$ .
- Each double bond or ring reduces the hydrogen count by 2 compared to a fully saturated alkane.
- Example: For molecular formula C6H10, $DOU = 2$ , indicative of 2 double bonds/rings.
Considerations: Include effects of Group V (nitrogen), Group VI (oxygen, sulfur), and Group VII (halogens). Adjust hydrogen counts accordingly.

Functionality: Provides information on the mass of compounds and their fragments.
Process:
- Ionization: Molecules are ionized and fragmented.
- Separation based on mass-to-charge ratio (m/z).
- The molecular ion peak (M+) is crucial as it reflects the molecular mass, typically the heaviest ion detected.
Chemistry Challenge: Determining structures and potential impurities based on mass spectra obtained for compounds like amphetamine.

Bond Vibrations: Stronger bonds and lighter atoms vibrate at higher frequencies. Infrared radiation causes excitation of vibrations in bonds with a dipole.
- No dipole means no vibration in response to IR.
Spectrometer Components:
- High-quality infrared light source, slit for beam creation, sample carrier, and detector.
Spectrum Characteristics:
- Bonds absorb IR radiation at distinct energies reflected in unique absorption bands.
- Absorption bands are stated in wavenumbers (cm-1).
- Non-polar bonds do not generate bands in the IR spectrum.

Regions of Interest: Various functional groups absorb IR at specific wavenumbers:
- O-H (alcohols): 3200–3600 cm-1
- C=O (carboxylic acid): 1710-1800 cm-1
- C-H (sp3): 2800–3000 cm-1
Application: Utilize correlation tables for IR bands during compound identification.

Chemical Shift: Charges from nuclear spin states influence signals detected in NMR.
Electronegativity Effects: Electronegative atoms deshield hydrogens, altering their resonance frequency and moving their signals toward higher ppm values.

Significance: NMR has dramatically influenced organic chemistry for structural elucidation.
Principle: Nuclei with spin produce a magnetic moment. In a magnetic field, these align to either lower or higher energy states (spin states).
- Excitation: Electromagnetic radiation can transition these nuclei from low to higher states (spin-flip), detected to reveal molecular environments.

Types of Information Extracted:
1. Hydrogen Types: Number of signals corresponds to the number of different hydrogen environments.
2. Integration: Peak area ratios reflect the number of each type of hydrogen.
3. Chemical Shift Analysis: Reflects hybridization and surroundings (presence of functional groups) affecting hydrogen environments.
Chemical Shift Values are reported in ppm, relative to tetramethylsilane (TMS).

Different functional groups resonate at characteristic shifts:
- Ethyl protons: 0.9-1.7 ppm
- Vinyl protons: 4.0-7.0 ppm
- OH and NH: 1–5 ppm (broad range)
- Aldehyde protons: 9.0-10.0 ppm
Protons close to electronegative groups or within aromatic systems shift higher due to deshielding effects.

In-class and take-home problems involving structure assignments from NMR and IR spectra.
Challenge scenarios based on real-world applications of spectroscopy in pharmaceuticals and synthetic chemistry, including the differentiation between similar compounds based on spectral data.

IR and NMR spectroscopy serve fundamental roles in molecular structure determination, impacting both academic research and practical applications in pharmaceuticals, food safety, and environmental chemistry. This foundational knowledge is critical for effective analysis in organic chemistry.