Chem 234 Exam 1 Questions With 100% Correct Answers

Chem 234 Exam 1 Questions With 100% Correct Answers Allows us to determine the molecule mass and the molecular formula of a compound, as well as some of it's structural features - answerMass Spectrometry Tells us the kinds of functional groups a compound has - answerInfrared (IR) Spectroscopy Provides information about the carbon-hydrogen framework of an organic compound - answerNuclear magnetic resonance (NMR) spectroscopy A very small sample is placed in a mass spectrometer, where it is vaporized and then ionized (electron removed from each molecule). Electron ionization (EI) bombards the vaporized molecules with a beam of high-energy electrons which knocks out an electron, producing a molecular ion (radical cation). The bombardment injects so much kinetic energy that the molecular ions fragment. All the positively charged fragments are drawn between two negatively charged plates, which push them into a analyzer tube that is surrounded by a magnet. The magnetic field deflects the positively charged fragments in a curved path depending on mass-to- charge ratio (M/z). The particles with the same m/z can be separated. The strength of the magnetic field is increased so progressively larger m/z values are guided through - answerMass Spectroscopy Typical beam strength in Mass spectroscopy - answer70 electron volts a species with an unpaired electron and a positive charge - answerradical cation (molecular ion) The path of a fragment with a smaller m/z will bend ____ than that of a heavier fragment - answermore A graph of the relative abundance of each fragment plotted against it's m/z value - answerMass Spectrum Seince the charge (z) of all fragments is essentially +1, m/z is the ____? - answermass (m) The peak with the highest m/z value is the _____? - answermolecular ion The m/z value of the molecular ion (highest m/z) gives the _____ - answermolecular mass Peaks with smaller m/z values -- represent positively charged fragments of the molecular ion - answerFragment ion peaks Tallest peak -- it has the greatest relative abundance because it is generally the most stable positively charged fragment (assigned 100% abundance) - answerBase peak The relative abundance of each of the other peaks is shown as a percentage of the ____ - answerbase peak When breaking bonds, resulting in primary carbocation and a primary radical is ____ favorable then ending with a methyl carbocation/radical - answerMORE Tertiary carbocations is the _____ stable - answermost Weaker bonds will fragment first, and bonds that break to form more stable fragments break in preference than those that form less stable fragments - answerFragmentation rules Allows possible molecular formulas to be determined from the m/z value of the molecular ion - answerRule of 13 Dividing m/z value of the molecular ion by 13 to determine number of carbons - answerBase value Divide the m/z value by 13 to get the number of C and a remainder. Add the remainder to the number of C's to find the number of H's. (142/13 = 10 with 12 remaining --- C10H22) - answerRule of 13 If the compound has an oxygen, than an O must be added and ______ must be subtracted - answerOne C and 4 H's states that if a compound has a molecular ion with an odd-numbered mass, the compound contains an odd number of nitrogen atoms - answerNitrogen rule Very small peak one unit greater (heavier) than the molecular ion - answerM+1 peak M+1 peak owes it presence to the fact that there are two naturally occurring isotope of carbon: - answer12C and 13C Any molecule containing 13C will appear at - answerM+1 Very small peaks at M+2 tend to account for - answer18O isotope If M+2 peak is one third the height of the molecular ion peak, then the compound contains a _____ atom because of the natural abundance of 37Cl is one-third that of 35Cl - answerChlorine If M and M+2 peaks are about the ska heigh then the compound contains a _____ atom because the natural abundances of 79Br and 81 Br are about the same - answerBromine Can determine exact mass of a fragment to the