Analytical Chemistry: Spectroscopy Techniques

UV-Vis spectroscopy measures the absorption of energy by electrons in molecules causing transitions to higher energy levels, while IR spectroscopy measures the absorption of energy by molecular vibrations.

The acronym 'm/z' represents the mass-to-charge ratio of an ion. It is a key parameter in mass spectrometry, as it allows for the identification and characterization of ions based on their mass and charge.

The (M+1) peak represents the presence of a heavier isotope of the molecule, usually due to the incorporation of Carbon-13 instead of Carbon-12. It provides information about the isotopic composition of the molecule.

<p>The base peak is the most intense peak in a mass spectrum, representing the ion that is most readily formed and stable in the gas phase. It is used as a reference point to determine the relative abundance of other ions in the spectrum.</p> Signup and view all the answers

<p>The steps include ionization of the organic compound in the gas phase, usually via electron ionization, separation of the resulting ions by their mass-to-charge ratio (m/z) using a magnetic or electric fields, and detection of the ions to produce the mass spectrum.</p> Signup and view all the answers

<p>Mass spectrometry differs from UV-Vis and IR spectroscopy by not using electromagnetic radiation. Instead, it relies on the ionization and separation of molecules based on their mass-to-charge ratio.</p> Signup and view all the answers

<p>Mass spectrometry can be used to determine the molecular weight of compounds, which is critical for identifying unknowns. It can also be used to identify components in a complex mixture, such as in environmental samples or biological fluids.</p> Signup and view all the answers

<p>Neutral particles are not detected in mass spectrometry because the technique relies on the separation and detection of ions, which are charged particles. Neutral particles do not interact with the electric or magnetic fields used in the instrument.</p> Signup and view all the answers

<p>Mass spectrometry provides valuable information about the molecular weight and fragmentation patterns of unknown compounds, enabling the identification of functional groups and structural features.</p> Signup and view all the answers

<p>Mass spectrometry can distinguish between molecules of similar relative molecular mass by analyzing their fragmentation patterns. Each molecule will fragment in a unique way, resulting in different peaks in the mass spectrum.</p> Signup and view all the answers

<p>The heated cathode emits high-energy electrons that collide with the sample molecules, causing ionization.</p> Signup and view all the answers

<p>The m/z value represents the ratio of the ion's mass to its charge, which helps identify the ion's composition and structure.</p> Signup and view all the answers

<p>Ionization occurs when high-energy electrons from the cathode collide with sample molecules, knocking out one or more electrons. This process creates positive ions (cations).</p> Signup and view all the answers

<p>Electron impact ionization is a common technique where high-energy electrons bombard the sample, causing fragmentation and the formation of radical cations.</p> Signup and view all the answers

<p>The major stages are vaporization, ionization, acceleration, deflection, and detection. Vaporization prepares the sample for ionization. Ionization creates charged ions. Acceleration speeds up the ions. Deflection separates the ions by their mass-to-charge ratios. Detection measures the abundance of ions.</p> Signup and view all the answers

<p>The magnetic field deflects the ions based on their mass-to-charge ratio, separating them according to their unique m/z values.</p> Signup and view all the answers

<p>Fragmentation produces a characteristic pattern of ions with different m/z values. These ions are detected and their abundance is plotted against their mass-to-charge ratios, creating a mass spectrum.</p> Signup and view all the answers

<p>Cations (positive ions) are typically detected because they are accelerated towards the detector by the electric field. The charge of an ion is important for its behavior in the mass spectrometer, as it governs the extent to which the ion is deflected by the magnetic field.</p> Signup and view all the answers

<p>A radical cation is a positive ion that has an unpaired electron, while a regular cation has all of its electrons paired. The unpaired electron in a radical cation introduces additional instability and reactivity.</p> Signup and view all the answers

<p>The abundance of each ion is represented by the height of the peak in the mass spectrum. The abundance of each fragment ion provides information about the relative stability and ease of formation of the corresponding fragments, offering clues about the molecule's structure and bonding.</p> Signup and view all the answers

<p>The molecular ion peak (M) represents the ion formed when the molecule loses one electron. It is the heaviest ion in the spectrum and usually has the highest m/z value. The base peak, on the other hand, is the most abundant fragment ion, which corresponds to the tallest peak in the mass spectrum. It indicates the most stable fragment ion.</p> Signup and view all the answers

<p>The M+1 peak is caused by the presence of isotopes, particularly the heavier isotopes of carbon (¹³C) and hydrogen (²H). These isotopes contribute to the overall molecular weight of the molecule, resulting in a peak one mass unit higher than the molecular ion peak.</p> Signup and view all the answers

<p>Isotopes can be used to confirm the presence of specific elements in a compound. By analyzing the relative abundance of isotopes in the mass spectrum, we can determine the presence and quantity of specific elements. For example, the ratio of peaks containing bromine and its isotope ¹³Br (100/98) confirms the presence of bromine in a compound.</p> Signup and view all the answers

<p>More stable carbocations tend to be more abundant in the mass spectrum, resulting in higher peaks at their corresponding m/z values. This is because stable carbocations are less likely to fragment further, leading to a greater accumulation of those ions.</p> Signup and view all the answers

<p>The molecular ion of 2-methylbutan-2-ol is unstable due to branching at the carbon atom where the positive charge resides. This instability leads to rapid fragmentation and hence, the absence of a significant molecular ion peak. In contrast, pentan-2-ol, being a straight-chain alcohol, has a more stable molecular ion, resulting in a noticeable peak in its mass spectrum.</p> Signup and view all the answers

<p>Mass spectrometry has a wide range of applications, including determining relative isotopic masses and isotopic abundance, distinguishing between molecules of similar molecular weight, identifying unknown compounds by their fragmentation patterns, carbon dating, and forensic science.</p> Signup and view all the answers

<p>A mass spectrometer works by ionizing a sample and then separating the resulting ions based on their mass-to-charge ratio. The sample is first vaporized and then ionized, often by electron bombardment. These ions are then accelerated through an electric field and passed through a magnetic field. The magnetic field deflects the ions according to their mass-to-charge ratio, resulting in a spectrum of peaks corresponding to different ions.</p> Signup and view all the answers

<p>The molecular ion peak (M) provides the molecular weight of the compound under investigation. It's the heaviest ion formed in the spectrum and often gives the molecular formula of the compound.</p> Signup and view all the answers

<p>Fragmentation is a key aspect of mass spectrometry as it generates characteristic fragments that provide valuable information about the structure and composition of the molecule. The patterns of fragments and their abundance at different m/z values help identify the compound and its structural features.</p> Signup and view all the answers

<p>The fragmentation pattern of a molecule in a mass spectrum is often unique and characteristic, allowing for its identification. By analyzing the mass-to-charge ratio of the fragments and their relative abundances, we can deduce the compound's structure, functional groups, and bonding arrangements. Each compound tends to produce its own distinct fragmentation pattern, serving as its chemical fingerprint.</p> Signup and view all the answers

Analyzes absorption of UV and visible light causing electron excitation in molecules.

Involves absorption of IR light causing molecular vibrations in covalent bonds.

An analytical technique to determine molecular weights and identify substances without radiation.

The process of converting atoms or molecules into charged ions for mass spectrometry.

A key measurement in mass spectrometry representing ion mass divided by charge.

The tallest peak in a mass spectrum representing 100% relative abundance of ions.

A peak in mass spectra indicating the presence of isotopes, specifically one mass unit more than the M peak.

Percentage of each ion's signal compared to the base peak in a mass spectrum.

A method to produce gas phase ions by bombarding with electrons in mass spectrometry.

Uncharged particles that are not detected in mass spectrometry.

The peak representing the molecular ion formed by losing one electron from the molecule.

Ions formed from the fragmentation of the molecular ion in mass spectrometry.

The relative amount of different isotopes of an element in a sample.

Carbocations that are less reactive and more abundant in mass spectroscopy.

The sum of the atomic masses of the atoms in a molecule used for identification.

A graphical representation of the mass-to-charge ratios of ions produced during mass spectrometry.

Techniques used in fields such as forensic science, drug discovery, and isotopic dating.

Identification of methyl bromide through peak ratios of Br and its isotope 81Br in mass spectrometry.

An ion formed from the entire molecule after ionization.

A measurement used to separate ions based on their mass and charge.

Ions gain kinetic energy through an electric field.

The bending of ions' paths due to a magnetic field.

A method where high-energy electrons create ions by dislodging others.

A positively charged ion with an unpaired electron.

The component that measures and records the abundance of ions.