Presentation on theme: "14-1 Prepared By Dr. Khalid Ahmad Shadid Islamic University in Madinah Department of Chemistry CH-4 Part 2 Mass Spectroscopy."— Presentation transcript:
14-1 Prepared By Dr. Khalid Ahmad Shadid Islamic University in Madinah Department of Chemistry CH-4 Part 2 Mass Spectroscopy
14-2 MASS 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
14-3 Molecules with Heteroatoms Isotopes are present in their usual abundance. Carbon has a 13 C isotope present in 1.1% abundance. The spectrum will show the normal M + and small M+1 peak. Bromine has two isotopes: 79 Br (50.5%) and 81 Br (49.5%). Since the abundances are almost equal, there will be an M + peak and and M+2 peak of equal height.
14-4 Mass Spectrum with Bromine Bromine is a mixture of 50.5% 79 Br and 49.5% 81 Br. The molecular ion peak M + has 79 Br be as tall as the M+2 peak that has 81 Br.
14-5 Mass Spectrum with Chlorine Chlorine is a mixture of 75.5% 35 Cl and 24.5% 37 Cl. The molecular ion peak M + is 3 times higher than the M+2 peak.
14-6 Mass Spectrum with Sulfur Sulfur has three isotopes: 32 S (95%), 33 S (0.8%), and 34 S (4.2%). The M + peak of ethyl methyl sulfide has an M+2 peak that is larger than usual (about 4% of M + ).
14-7 Hexane (m/z = 86 for parent) has peaks at m/z = 71, 57, 43, 29 Alkanes --- Fragmentation of Hexane CH 3. - CH 3 CH 2. - CH 3 CH 2 CH 2. -
14-9 Mass Spectrum of n-Hexane Groups of ions correspond to loss of one-, two-, three-, and four-carbon fragments.
14-10 Fragmentation of Branched Alkanes The most stable carbocation fragments form in greater amounts.
14-11 Alkanes Figure 14.6 Mass spectrum of 2,2,4-trimethylpentane.
14-12 Mass Spectra of Alkenes Alkenes characteristically: Show a strong molecular ion peak. Cleave readily to form resonance-stabilized allylic cations.
14-13 Alkynes 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.
14-14 Alcohols One of the most common fragmentation patterns of alcohols is loss of H 2 O 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) A radical + + OHC R + R'-COH A resonance-stabilized oxonium ion R R" R' R" R'-C=O-H R" +
14-15 Alcohols Figure 14.10 Mass spectrum of 1-butanol.
14-21 Esters -cleavage and McLafferty rearrangement
14-22 Esters Figure 14.13 Mass spectrum of methyl butanoate. m/z 102 = molecular ion m/z 74 = McLafferty rearrangement m/z 71 and 59 = the result of cleavage
14-23 Aromatic Hydrocarbons Most show an intense molecular ion peak. Most alkylbenzenes show a fragment ion of m/z 91. Figure 14.14 Mass spectrum of toluene.
14-24 Amines Figure 14.15 Mass spectrum of 3-methyl-1- butanamine. The most characteristic fragmentation pattern of 1°, 2°, and 3° aliphatic amines is -cleavage.
14-25 Problem 14.31 2-Methylpentanal and 4-methyl-2-pentanone are constitutional isomers with the molecular formula C 6 H 12 O. Each shows a molecular ion in its mass spectrum at m/z 100. 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.
14-26 Problem 14.31 The 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
14-27 قواعد التكسير جذر كاتيوني عدد فردي من اللالكترونات جزيئ متعادل عدد زوجي من اللالكترونات كاتيون جذر حر كاتيون جزيئ متعادل عدد زوجي من اللالكترونات