4.2.4 - Analytical Techniques Flashcards
What is the purpose of analytical techniques in organic chemistry?
Analytical techniques are used to identify and characterize the structure of organic compounds, determine their purity, and identify functional groups present in the molecules.
What is infrared (IR) spectroscopy used for in organic chemistry?
IR spectroscopy is used to identify functional groups in organic molecules by measuring the absorption of infrared radiation, which causes bonds in the molecule to vibrate at characteristic frequencies.
How does IR spectroscopy work?
In IR spectroscopy, a sample is exposed to infrared radiation, and the frequencies at which the sample absorbs radiation correspond to the vibrational frequencies of different bonds within the molecule. These are plotted on an absorption spectrum.
What are fingerprint regions in IR spectra?
The fingerprint region (typically between 1500–500 cm⁻¹) contains unique absorption bands specific to a molecule. It is used to identify compounds by comparing the spectrum with known standards.
What does the O-H stretch in an IR spectrum indicate?
The O-H stretch typically appears as a broad, strong absorption band around 3200–3550 cm⁻¹, indicating the presence of a hydroxyl group (-OH), such as in alcohols or carboxylic acids.
What does the C=O stretch in an IR spectrum indicate?
The C=O stretch appears as a strong absorption band around 1650–1750 cm⁻¹, indicating the presence of a carbonyl group, as in aldehydes, ketones, or carboxylic acids.
What is nuclear magnetic resonance (NMR) spectroscopy used for?
NMR spectroscopy is used to determine the structure of organic compounds by analyzing the magnetic properties of nuclei, typically ¹H (proton) and ¹³C (carbon) nuclei, in a magnetic field.
How does ¹H NMR spectroscopy work?
In ¹H NMR, the sample is exposed to a strong magnetic field, and the protons (hydrogens) in the sample absorb radiofrequency radiation at specific frequencies. These frequencies are dependent on the chemical environment of the protons.
What does the chemical shift in an NMR spectrum tell us?
The chemical shift (measured in parts per million, ppm) indicates the environment of the hydrogen or carbon nuclei. Different functional groups and atoms around the nucleus affect the chemical shift.
What does a splitting pattern (multiplet) in a proton NMR spectrum represent?
The splitting pattern (e.g., doublet, triplet, quartet) results from the interaction of a proton with adjacent protons. This helps determine the number of neighboring protons and provides insight into the molecular structure.
What is ¹³C NMR spectroscopy used for?
¹³C NMR is used to identify the types of carbon atoms in a molecule by analyzing the magnetic environments of ¹³C nuclei. This helps determine the carbon skeleton of the compound.
What is the importance of the integration of peaks in NMR spectra?
The integration of peaks indicates the relative number of protons (in ¹H NMR) or carbons (in ¹³C NMR) in the sample. The area under each peak is proportional to the number of equivalent protons or carbons.
What is mass spectrometry (MS) used for in organic chemistry?
Mass spectrometry (MS) is used to determine the molecular mass and structure of a compound by measuring the mass-to-charge ratio (m/z) of ions produced by the sample.
How does mass spectrometry work?
In mass spectrometry, the sample is ionized to produce charged particles (ions). These ions are then accelerated through a magnetic field, and their mass-to-charge ratios are measured to produce a mass spectrum.
What is the molecular ion peak in a mass spectrum?
The molecular ion peak (also known as the M+ peak) represents the ion corresponding to the entire molecule. The position of this peak gives the molecular mass of the compound.
What is fragmentation in mass spectrometry?
Fragmentation occurs when the molecular ion breaks into smaller ions (fragments) under the influence of the mass spectrometer. These fragments help in deducing the structure of the compound.
What is the base peak in a mass spectrum?
The base peak is the tallest peak in the spectrum, representing the most abundant ion produced during ionization. Its intensity is assigned a value of 100, and other peaks are measured relative to it.
How is ultraviolet (UV) spectroscopy used in organic chemistry?
UV spectroscopy is used to identify compounds that absorb UV light. The absorption corresponds to electronic transitions within molecules, particularly for compounds with conjugated double bonds or aromatic systems.
What does a UV absorption spectrum tell you?
The UV absorption spectrum provides information about the wavelengths of light absorbed by a compound. The position of absorption bands is related to the energy gap between molecular orbitals, which can help identify functional groups and structural features.
What is thin-layer chromatography (TLC) used for?
TLC is used to separate and identify compounds based on their differing polarities. A small sample is spotted on a plate coated with a thin layer of adsorbent, and compounds are separated as they move through the stationary phase.
