Ch. 15 - Analytical Techniques: IR, NMR, Mass SpectSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Concept #1: The (M + 1) Peak

Concept #2: The (M + 2) Peak

Concept #3: The Nitrogen Rule

Practice: Propose the number of carbons for a compound that exhibits the following peak in its mass spectrum: 

(M)+• at m/z = 72, relative height = 38.3% of base peak

(M+1)+• at m/z = 73, relative height = 1.7% of base peak 

Practice: Predict the approximate height of the (M + 1) peak for the molecule icosane, molecular formula C20H42.

Concept #4: Draw expected isotope pattern Intro

Practice: Draw the expected isotope pattern that would be observed in the mass spectrum of CH2Br2. In other words, predict the relative heights of the peaks at M, (M + 2), and (M + 4) peaks.

Additional Problems
Compounds containing chlorine or bromine usually show a strong _____ peak. a) M+2 b) molecular ion c) base d) M+1 e) all of these
Which of the following exists as two naturally occuring isotopes separated in mass by two amu and therefore shows an (M+2)+ peak roughly 1/3 as intense as M + in the mass spectrum.  a) Bromine b) Chlorine c) Nitrogen d) All of the above e) None of the above
The formula of a compound with an even massed molecular ion will a) contain an even number of nitrogen atoms. b) contain an even number of halogen atoms. c) contain an odd number of nitrogen atoms. d) produce even massed fragment ions from one bond cleavage processes. e) none of the above.
Which of the following compounds will have an odd m/z value for the molecular ion? a) I b) II c) III d) IV
Which compound below is expected to show an odd molecular ion in the mass spectrum and two IR signals between 3300 and 3500 cm-1? a) H2NCH2CH2CH2CH2CH2CH2NH2 b) Diethylamine c) Ethylamine d) All of the above e) None of the above
Which of the following mass spectra shows the presence of bromine in a compound? a I b II   c III   d IV e none of these
For which of the following compounds will the (M+2) + peak intensity be around one third the intensity of the molecular ion peak? a CH3CH2CH2Br  b CH3CH2CH2OH  c CH3CH2CH2Cl  d CH3CH2CH2NH2  e none of these
Indicate which spectral technique, NMR, UV, or MS, would most readily allow differentiation between compounds. a. NMR b. UV c. MS
It is possible to identify that a given compound contains either chlorine or bromine from the presence of M and (M+2) peaks in the mass spectrum of the compound. State what species causes the (M+2) peaks in each of the following compounds.   (i) C3H7Cl   (ii) C2H5Br
Propose a molecular formula that is consistent with the following mass spectrum data:(M)+• at m/z = 78, relative height=23.5%(M+1)+• at m/z = 79, relative height=0.78%(M+2)+• at m/z = 80, relative height=7.5%