Name: cycloalkane ions and mass peaks
Uploaded: 2024-12-05T18:32:19.000Z
Duration: 1 min 5 s
Channel: JoVE

Sikloalkan moleküler iyonları, doğrusal veya dallı alkan moleküler iyonlarından daha kararlıdır.
Örneğin, 84 kütle-yük oranındaki sikloheksan moleküler iyon sinyali, hekzanın moleküler iyon zirvesinden daha güçlü yoğunluk gösterir.
Siklohekzanın moleküler iyonu, bir etilen molekülü ve kütle-yük oranı 56 olan yeni bir radikal katyon üretmek üzere parçalanır. Bu radikal katyon nispeten kararlıdır ve spektrumun temel zirvesidir. 
Dallanmış sikloalkanlarda, etilene parçalanma ve bir bütil radikal katyonu dışında, başka bir parçalanma, moleküler iyondan yan zincirin kaybını zorlar. Örneğin, metil siklopentan moleküler iyonu, siklopentil katyonunu oluşturmak için metil yan zincirini kaybeder.
Siklopentil katyonu ayrıca bir etilen molekülü ve bir propil radikal katyonu elde etmek için parçalanmaya uğrar.

kütle spektrometrisi: sikloalkan parçalanması

Mass Spectrometry: Cycloalkane Fragmentation

Kütle spektrometrisinde sikloalkanlar, doğrusal veya dallanmış alkanlara kıyasla moleküler iyonlarının doğal kararlılığı nedeniyle belirgin parçalanma desenleri sergiler. Sikloalkanların halka yapısı, moleküler iyonlara ek kararlılık sağlar ve genellikle kütle spektrumunda belirgin iyon tepeciklerine neden olur.

Örneğin, sikloheksan moleküler iyonlarının kütle-yük oranı (m/z) 84'tür ve bu da heksan gibi doğrusal alkanlardan daha güçlü bir sinyal üretme eğilimindedir. Bu kararlılık, iyonu sabitleyen kapalı halka yapısından gelir. Sikloheksan için yaygın bir parçalanma yolu, bir etilen molekülünün (C_2H_4) kaybını içerir ve geride m/z'si 56 olan bir radikal katyon bırakır. Bu sonuçtaki katyon oldukça kararlıdır ve sıklıkla kütle spektrumundaki en yoğun sinyal olan temel tepeyi oluşturur.

<img alt="Figure1" src="/files/ftp_upload/13042/13042-PT_Figure_1.svg" style="text-align: center; height: 80px;">

Şekil 1. Sikloheksan moleküler iyonunun parçalanması.

Metil siklopentan gibi dallı sikloalkanlar, yan zincirler nedeniyle ek parçalanma yolları sergiler. Tipik etilen kaybının yanı sıra, moleküler iyon ayrıca bir metil grubu (CH_3) gibi yan zincirleri de kaybedebilir. Örneğin, moleküler iyon bir metil radikalini (CH_3•) kaybedebilir ve bu da bir siklopentil katyonuyla sonuçlanır. Bu siklopentil katyonu daha fazla parçalanır ve tipik olarak etilen kaybına yol açar ve bu da kararlı bir propil radikal katyonuyla sonuçlanır.

Bu parçalanma desenleri, halka yapılarının ve dallanmanın kütle spektrometresinde iyon kararlılığını nasıl etkilediğini gösterir. Etilen ve yan zincirler gibi küçük moleküllerin karakteristik kaybı, spektrumda belirgin tepe noktaları olarak gözlemlenen oldukça kararlı katyonlar üretir.

<img alt="Figure2" src="/files/ftp_upload/13042/13042-PT_Figure_2_.svg" style="text-align: center; height: 180px;">

Şekil 2. Metil siklopentanın (üstte) eten ve bir bütil radikal katyonuna; (altta) bir metil radikaline ve bir siklopentil karbokasyonuna parçalanması, ardından siklopentil karbokasyonunun daha fazla parçalanması.

Kütle Spektrometrisi: Sikloalkan Parçalanması

Kütle spektrometresinde, sikloalkanlar, moleküler iyonlarının doğrusal veya ...

mass-spectrometry-cycloalkane-fragmentation

Education

JoVE Core

Analytical Chemistry

Analitik Kimya

Unit 1

Ünite 1

Mass Spectrometry Fragmentation Methods

Kütle Spektrometrisi Parçalanma Yöntemleri

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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, which makes the molecular ion more stable.

A common fragmentation path for cyclohexane is the loss of ethylene, C2H4. After this loss, a radical cation with an m/z of 56 remains. This ion is highly stable and often becomes the base peak, which is the most intense peak in the spectrum.

Branched cycloalkanes, such as methyl cyclopentane, can fragment in more than one way because of the side chain. Along with the usual loss of ethylene, the molecular ion may also lose a methyl group, CH3. This can form a cyclopentyl cation.

The cyclopentyl cation can fragment again. It usually loses ethylene and forms a stable propyl radical cation. These patterns show how ring size and branching affect ion stability. The loss of small molecules like ethylene and side chains often produces the most prominent peaks.

Cycloalkane Ions and Mass Peaks

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...

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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

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,...

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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...

mass spectrometry: cycloalkene fragmentation

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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...

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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...

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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...

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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...

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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...

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Carbonyl Fragment Patterns in Mass Spectra

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Mass Spectra of Carboxylic Compounds

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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...

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How MALDI Turns Samples Into Ions

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key terms and concepts

See how cycloalkanes fragment in mass spectrometry, from the stable cyclohexane molecular ion to ethylene loss and peaks from branched rings.

Cycloalkane Ions and Mass Peaks | JoVE K12

JoVE Core Analitik Kimya, karmaşık kimyasal prensiplerini anlaşılır, ilgi çekici animasyonlara dönüştürerek basitleştirir ve SI Birimlerinden NMR spektroskopisine kadar konuları daha erişilebilir ve anlaşılır hale getirir. Buna ek olarak, bilim insanlarının yer aldığı videolar, bu kavramların dünya çapındaki laboratuvarlarda yürütülen gerçek dünya araştırmalarındaki uygulamalarını gösterir.

Cycloalkane Ions and Mass Peaks

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