Name: alkene ion fragmentation patterns
Uploaded: 2024-12-05T18:32:19.000Z
Duration: 59 s
Channel: JoVE

이온화되면 알켄의 파이 결합에서 하나의 전자가 변위되어 분자 이온을 형성합니다.
2-methyl-1-pentene의 경우와 같이, 분자 이온의 질량 신호는 알켄을 위해 두드러집니다.
알켄 분자 이온에서 널리 사용되는 단편화 경로는 알릴 단편이 공진에 의해 안정화되기 때문에 알릴 위치에서 절단하는 것입니다.
불포화 결합에 인접한 탄소-탄소 결합에서 교대 단편화가 발생하여 알케닐 탄소양이온과 해당 알킬 라디칼이 생성됩니다.
이중 결합에 대해 γ 수소를 갖는 알켄은 McLafferty 재배열을 거쳐 저분자량 알켄 라디칼 양이온 및 알켄을 생성합니다.
거의 동일한 질량 신호를 사용하여 알켄의 위치 및 기하학적 이성질체를 구별하는 것은 어렵습니다.

질량분석법: 알켄 단편화

Mass Spectrometry: Alkene Fragmentation

알켄은 이온화 시 불포화 π 결합에서 전자 1개를 잃고 안정적인 분자 이온을 형성합니다. 알켄의 추가 단편화는 세 가지 다른 반응 경로를 통해 발생합니다. 가장 눈에 띄는 단편화는 알릴 위치에서의 절단입니다. 생성된 알릴성 탄수화물은 공명 안정화됩니다. 말단 알켄의 질량 스펙트럼에서 이 조각은 41의 질량 대 전하 비율로 나타납니다. 두 가지 알릴 절단 선택이 있는 내부 알켄에서 절단은 우선적으로 부산물로서 더 치환된 알킬 라디칼을 생성합니다. . 그림 1은 알릴 위치에서 2-메틸-1-펜텐의 단편화를 보여줍니다.

<img alt="Figure1" src="/files/ftp_upload/13043/13043_PT_Figure_1.svg" style=" height: 80px;">

그림 1. 알릴 위치에서 2-메틸-1-펜텐의 단편화.

또 다른 단편화 경로는 불포화 결합에 인접한 탄소-탄소 결합에서 발생하여 알케닐 탄소양이온과 상응하는 알킬 라디칼을 생성합니다. 단편화는 바람직하게는 보다 안정한 알킬 라디칼을 생성하기 위해 발생한다. 예를 들어, 2-메틸-1-펜텐의 단편화는 그림 2에 표시된 것처럼 불포화 결합의 양쪽에서 발생할 수 있습니다. 생성된 알케닐 탄수화물의 질량 신호는 그림 3에 표시되어 있습니다. 상대 강도는 단편화가 프로페닐로 이어지는 것을 보여줍니다. 양이온 및 프로필 라디칼이 선호됩니다.

<img alt="Figure2" src="/files/ftp_upload/13043/13043_PT_Figure_2.svg" style=" height: 165px;">

그림 2. 불포화 결합의 인접한 탄소에서 2-메틸-1-펜텐의 단편화.

<img alt="Figure3" src="/files/ftp_upload/13043/13043_PT_Figure_3.svg" style=" height: 135px;">

그림 3. 2-메틸-1-펜텐의 질량 스펙트럼.

불포화 결합에 대해 γ 수소를 갖는 알켄은 맥라페르티 재배열을 겪습니다. 맥라페르티 재배열은 γ 수소가 고리형 6원 고리의 이중 결합으로 이동할 때 발생합니다. 이로 인해 α-탄소와 β-탄소 사이의 결합이 절단되어 두 개의 조각, 즉 저분자량 알켄 라디칼 양이온과 중성 알켄이 생성됩니다. 질량 분석법에서 중요한 이러한 재배열은 특정 조각 이온을 생성하여 알켄의 구조를 식별하는 데 도움이 됩니다. 그림 4는 맥라페르티 재배열을 통한 2-메틸-1-펜텐의 단편화를 보여줍니다.

<img alt="Figure4" src="/files/ftp_upload/13043/13043_PT_Figure_4.svg" style=" height: 92px;">

그림 4. McLafferty 재배열을 통한 2-메틸-1-펜텐의 단편화.

알켄은 이온화 시 불포화 π 결합에서 하나의 전자를 잃고 안정적인 분자 이온을 형성합니다. 알켄의 추가 단편화는 다음을 통해 발생합니다.

Education

교육

JoVE Core

Analytical Chemistry

분석 화학

Unit 1

제1단원

Mass Spectrometry Fragmentation Methods

질량 분석법의 단편화 방법

KEY TERMS AND CONCEPTS

주요 용어 및 개념

alkene ion fragmentation patterns

Alkene ion fragmentation patterns in mass spectrometry begin when the molecule loses one electron from the unsaturated π bond. This ionization forms a stable molecular ion. The ion can then break apart by three main reaction pathways.

The most common pathway is cleavage at the allylic position, which is the carbon next to the double bond. This produces an allylic carbocation that is stabilized by resonance. In terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In internal alkenes, there are two possible allylic cleavages, and the preferred one gives the more substituted alkyl radical as the other product.

A second pathway breaks the carbon-carbon bond adjacent to the unsaturated bond. This forms an alkenyl carbocation and a matching alkyl radical. The cleavage usually happens in the direction that gives the more stable alkyl radical. For 2-methyl-1-pentene, this can occur on either side of the double bond, and the spectrum shows signals that favor the propenyl cation and propyl radical products.

A third pathway is the McLafferty rearrangement, which occurs in alkenes that have a γ hydrogen relative to the unsaturated bond. In this step, the γ hydrogen transfers to the double bond through a cyclic six-membered ring. The rearrangement then breaks the bonds between the α- and β-carbons. It produces a lower molecular weight alkene radical cation and a neutral alkene, which helps identify alkene structure in mass spectrometry.

Alkene Ion Fragmentation Patterns

mass spectrometry: long-chain alkane fragmentation

mass-spectrometry-long-chain-alkane-fragmentation

Mass Spectra of Linear Alkane Chains

Mass spectra of linear alkanes show a clear fragmentation pattern. The molecular ion often breaks at a carbon-carbon bond away from the end of the chain. This cleavage forms a stable carbocation and a stable radical, so the middle of the mass-to-charge plot usually has the strongest signals while the ends are weaker. As each bond breaks, a methyl group is lost and the main peaks in the spectrum appear 14 u apart. Smaller peaks near each main signal can also appear. These come from secondary...

mass spectrometry: branched alkane fragmentation

mass-spectrometry-branched-alkane-fragmentation

Branched Alkanes in Mass Spectra

Branched alkanes in mass spectrometry fragment quickly because branching can create stable carbocations. When cleavage happens at a branching point, a secondary or tertiary carbocation may form. That stability helps explain why the molecular ion peak is often very weak or missing compared with a linear alkane. The lesson uses 2-methylbutane, neopentane, and n-pentane to show how this pattern appears in mass spectra. 2-methylbutane and neopentane break apart to form secondary and tertiary...

mass spectrometry: cycloalkane fragmentation

mass-spectrometry-cycloalkane-fragmentation

Cycloalkane Ions and Mass Peaks

Cycloalkane ions in mass spectrometry often give strong peaks because the ring structure helps stabilize the molecular ion. Compared with linear or branched alkanes, this added stability changes how the molecule breaks apart. As a result, cycloalkanes can produce prominent signals in the mass spectrum. Cyclohexane is a clear example. Its molecular ion has an m/z of 84, and this peak is often stronger than the signal from hexane, a linear alkane. The closed ring helps hold the ion together,...

mass spectrometry: alkene fragmentation

Alkene ion fragmentation patterns in mass spectrometry begin when the molecule loses one electron from the unsaturated π bond. This ionization forms a stable molecular ion. The ion can then break apart by three main reaction pathways. The most common pathway is cleavage at the allylic position, which is the carbon next to the double bond. This produces an allylic carbocation that is stabilized by resonance. In terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In internal...

mass spectrometry: cycloalkene fragmentation

mass-spectrometry-cycloalkene-fragmentation

Cycloalkene Side-Chain Cleavage in Mass Spectra

Cycloalkenes can break apart in a mass spectrometer through retro-Diels–Alder fragmentation. In this process, two carbon-carbon bonds in the ring split, and ethene is released. The remaining fragment is a dienyl radical cation that is 28 u less than the molecular ion. This pathway is similar to the fragmentation of cycloalkanes that also releases ethene. The difference is the type of charged fragment that remains. Cycloalkanes form an alkyl species, while cycloalkenes form a dienyl species.

mass spectrometry: alkyne fragmentation

Alkyne Mass Spectra and Key Peaks

Alkyne mass spectra often show strong peaks from two main fragmentation paths. One path breaks the carbon-carbon bond between the alpha and beta carbons of the alkyne bond. This produces a 3-propynyl cation, also called a propargyl cation. In terminal alkynes, this is the only fragmentation path that gives the 3-propynyl cation. The unsubstituted 3-propynyl cation appears at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne forms a...

mass spectrometry: alcohol fragmentation

Alcohol Fragmentation Patterns in Mass Spectra

Alcohols fragment in mass spectrometry in predictable ways. When an alcohol, written as R-OH, ionizes, it can lose one non-bonded electron from the oxygen atom. That forms a molecular ion, but the molecular ion peak is often weak or may not appear because alcohols break apart quickly. Two main fragmentation routes are important for alcohols: β-cleavage and dehydration. In β-cleavage, the bond at the β-position next to the hydroxyl group breaks. This gives a resonance-stabilized cation and a...

mass spectrometry: aromatic compound fragmentation

mass-spectrometry-aromatic-compound-fragmentation

Mass Spectra of Benzene and Toluene

Mass spectra of aromatic compounds show a strong molecular ion peak. In ionization, the molecule becomes a molecular ion, which appears as a prominent peak in the spectrum. Benzene gives a molecular ion at m/z 78, and toluene gives one at m/z 92. Benzene’s molecular ion is especially stable. It does not fragment readily because breaking the aromatic benzene ring requires a large amount of energy. Alkyl-substituted benzenes behave differently in mass spectrometry. Toluene can lose a hydrogen...

mass spectrometry: amine fragmentation

Amines in Mass Spectra: Nitrogen Rule

Amines can be identified in mass spectrometry by their fragmentation patterns and by the nitrogen rule. The molecular ions of amines often break apart through β-cleavage, which cuts a carbon-carbon bond next to the nitrogen. This process forms an alkyl radical and a resonance-stabilized nitrogen-containing cation. The nitrogen rule helps predict the mass of the molecular ion. A compound with one nitrogen atom, or any odd number of nitrogen atoms, gives a molecular ion with an odd molecular...

mass spectrometry: alkyl halide fragmentation

mass-spectrometry-alkyl-halide-fragmentation

Mass Spectra of Alkyl Halides

Mass spectra of alkyl halides show clear isotope patterns from the halogen atom. Chlorine has two common isotopes, 35Cl and 37Cl, in a 3:1 ratio. Bromine has two common isotopes, 79Br and 81Br, in a 1:1 ratio. These isotope ratios create two molecular ion peaks, [M] and [M + 2], with relative heights that match the halide abundance. This pattern is easy to see in examples such as 2-chloropropane and 1-bromopropane. 2-Chloropropane gives peaks in a 3:1 ratio. 1-Bromopropane gives peaks in a 1:1...

mass spectrometry: aldehyde and ketone fragmentation

mass-spectrometry-aldehyde-and-ketone-fragmentation

Carbonyl Fragment Patterns in Mass Spectra

Aliphatic aldehydes and ketones break apart in mass spectrometry through a few key carbonyl fragment patterns. The main pathways are alpha-cleavage, inductive cleavage, and the McLafferty rearrangement. These patterns help chemists read the mass spectrum and spot a carbonyl group. Alpha-cleavage is a common break next to the carbonyl group. The bond beside the carbonyl splits, and this forms an alkyl radical and an acylium cation. The acylium cation is often seen in the spectrum because it is...

mass spectrometry: carboxylic acid, ester, and amide fragmentation

mass-spectrometry-carboxylic-acid-ester-and-amide-fragmentation

Mass Spectra of Carboxylic Compounds

Mass spectra of carboxylic acids, esters, and amides often show two key fragmentation routes: β-cleavage and McLafferty rearrangement. In β-cleavage, the carbon-carbon bond at the β-position next to the carboxylic group breaks. This produces a neutral radical and a cation. Long-chain compounds can also fragment by McLafferty rearrangement if they have a hydrogen on the γ-carbon. The γ-carbon is the third carbon away from the carboxylic group. This rearrangement gives a radical cation and a...

chemical ionization (ci) mass spectrometry

Using Reagent Gas in CI Mass Spectrometry

Chemical ionization mass spectrometry uses a reagent gas to help detect molecules that break apart too quickly in electron impact ionization. It is a milder ionization method that can extend the life of the ionized analyte, which makes molecular identification easier. In chemical ionization, the sample is mixed with an excess reagent gas. This setup makes the electron impact occur mainly on the reagent gas instead of on the analyte. The charged species formed from the reagent then protonates...

electrospray ionization (esi) mass spectrometry

electrospray-ionization-esi-mass-spectrometry

How ESI Turns Biomolecules Into Ions

Electrospray ionization, or ESI, is a mass spectrometry method used to detect biomolecules that are too large or nonvolatile for conventional electron impact ionization. These molecules may break down before they can ionize or evaporate. ESI helps prevent rapid fragmentation and lets scientists record a mass signal for the whole biomolecule. ESI uses electrical energy to move ions from the liquid phase into the gas phase. The analyte biomolecule is mixed with an ionic liquid, which is a...

matrix-assisted laser desorption ionization (maldi)

matrix-assisted-laser-desorption-ionization-maldi

How MALDI Turns Samples Into Ions

Matrix-assisted laser desorption ionization (MALDI) is a mass spectrometry technique that turns biomolecules into ions for analysis. It is used to identify and characterize proteins, peptides, nucleic acids, and carbohydrates. Because of this, it is common in biological and medical research, as well as pharmacology and biochemistry. In MALDI, the analyte of interest is mixed with a matrix material. The matrix is usually an organic compound, such as a small organic acid or a crystalline...

key terms and concepts

Learn how alkene ions break apart in mass spectrometry through allylic cleavage, adjacent bond cleavage, and McLafferty rearrangement for structure clues.

Alkene Ion Fragmentation Patterns | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Alkene Ion Fragmentation Patterns

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