Presentation on theme: "Infrared Spectroscopy. Prepared by Dr. Khalid A. Shadid"— Presentation transcript:
1Infrared Spectroscopy. Prepared by Dr. Khalid A. Shadid Islamic University in MadinahDepartment of ChemistryCH-4 Part 2 Mass SpectroscopyPrepared ByDr. Khalid Ahmad Shadid
2MASS SPECTROSCOPY مطياف الكتلة التعرف على الصيغة البنائية من خلال عمليات التكسير او تفكك المركب حطيمات - الجذر الكاتيوني غير ثابت بالتالي يتكسر او يتفكك الى ايونات او حطيمات صغيرة
3Molecules with Heteroatoms Isotopes are present in their usual abundance.Carbon has a 13C isotope present in 1.1% abundance. The spectrum will show the normal M+ and small M+1 peak.Bromine has two isotopes: 79Br (50.5%) and 81Br (49.5%). Since the abundances are almost equal, there will be an M+ peak and and M+2 peak of equal height.
4Mass Spectrum with Bromine Bromine is a mixture of 50.5% 79Br and 49.5% 81Br. The molecular ion peak M+ has 79Br be as tall as the M+2 peak that has 81Br.
5Mass Spectrum with Chlorine Chlorine is a mixture of 75.5% 35Cl and 24.5% 37Cl. The molecular ion peak M+ is 3 times higher than the M+2 peak.
6Mass Spectrum with Sulfur Sulfur has three isotopes: 32S (95%), 33S (0.8%), and 34S (4.2%).The M+ peak of ethyl methyl sulfide has an M+2 peak that is larger than usual (about 4% of M+).
7Alkanes --- Fragmentation of Hexane Hexane (m/z = 86 for parent) has peaks at m/z = 71, 57, 43, 29CH3. -CH3CH2. -CH3CH2CH2. -
9Mass Spectrum of n-Hexane Groups of ions correspond to loss of one-, two-, three-, and four-carbon fragments.
10Fragmentation of Branched Alkanes The most stable carbocation fragments form in greater amounts.
11AlkanesFigure 14.6 Mass spectrum of 2,2,4-trimethylpentane.
12Mass Spectra of Alkenes Alkenes characteristically:Show a strong molecular ion peak.Cleave readily to form resonance-stabilized allylic cations.
13Alkynes Alkynes typically Show a strong molecular ion peak. Cleave readily to form the resonance-stabilized propargyl cation or substituted propargyl cations.Figure 14.9 Mass spectrum of 12-pentyne.
14AlcoholsOne of the most common fragmentation patterns of alcohols is loss of H2O to give a peak which corresponds to M-18.Another common pattern is loss of an alkyl group from the carbon bearing the OH to give a resonance-stabilized oxonium ion and an alkyl radical.•Molecular ion(a radical cation)Aradical••+OHCR'-A resonance-stabilizedoxonium ion"=
22Esters Figure 14.13 Mass spectrum of methyl butanoate. m/z 102 = molecular ionm/z 74 = McLafferty rearrangementm/z 71 and 59 = the result of cleavage
23Aromatic Hydrocarbons Most show an intense molecular ion peak.Most alkylbenzenes show a fragment ion of m/z 91.Figure Mass spectrum of toluene.
24AminesFigure Mass spectrum of 3-methyl-1-butanamine. The most characteristic fragmentation pattern of 1°, 2°, and 3° aliphatic amines is -cleavage.
25Problem 14.312-Methylpentanal and 4-methyl-2-pentanone are constitutional isomers with the molecular formula C6H12O. Each shows a molecular ion in its mass spectrum at m/z Spectrum A shows significant peaks at m/z 85, 58, 57, 43, and 42. Spectrum B shows significant peaks at m/z 71, 58, 57, 43, and 29. Assign each compound its correct spectrum.
26Problem 14.31The expected -cleavage and McLafferty rearrangement fragmentations are:The -cleavage fragments at m/z 85 (Spectrum A) and 29 (Spectrum B) demonstrate that spectrum A corresponds to 4-methyl-2-pentanone, and Spectrum B corresponds to 2-methylpentanal.Insert
27قواعد التكسير جذر كاتيوني عدد فردي من اللالكترونات جزيئ متعادل عدد زوجي مناللالكتروناتكاتيونجذر حركاتيونجزيئ متعادلعدد زوجي مناللالكترونات