Lab Assignment 9

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Mesa Community College *

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116

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Chemistry

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Apr 3, 2024

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Chemical Thinking Lab Assignment 9 v1.2 | 1 Lab Assignment 9 Your name: ___Khanh Bui_______________________ Your section: ________ GRADE ____ /25 p All work must be very neat and organized . This assignment has an accompanying Lab Assignment 9 Guide and Lab Assignment 9 Data (separate documents on D2L). For the mass spectra, you are not expected to interpret all the fragmentation patterns. Rather, it is the parent (molecular ion) mass and fragmentation analysis to arrive at the base peak and phenyl (“benzene ring”) that matters. The latter analysis should assist in cases where several candidate structures are possible - only one structure should fit the analysis. Lab Assignment 9 concerns the analysis of FT-IR and MS spectra to infer the molecular structure of organic compounds. You can assume all the compounds are composed of carbon, hydrogen and possibly oxygen – but no other elements. Further, in the case of aromatic compounds (those with a “benzene ring”), assume a monosubstituted ring, meaning attachment to the ring occurs at only one ring carbon. In your analysis keep in mind carbon forms four bonds , oxygen two , and hydrogen just one . Double bonds count as “two bonds.” For example, with H 2 C=O, oxygen has “two bonds”, carbon four (two to oxygen and one each to two hydrogens) Problem 1 (7p). Using only the MS and FT-IR spectra of Unknown A determine the molecular structure of Unknown A . Clearly justify your structure using the available data. Your analysis must include the MS and FT-IR data. To receive credit, you must respond with well written, very legible, complete sentences that correctly employs chemical terminology and concepts. Mass spectral data: Molecular ion peak at (M/2)/58 58 – 43 = 15 = -CH3 Next Peak (base peak): 43 There is also a peak 29 43 – 29 = 14 = -CH2 Remaining 29, associated with – CHO So total structure: Molecular weight: 58 Is strongly evident by presence of peak in IR band at 1720 cm^-1 CHEM 151 LA 9 v1.2 MY © 2020 10-16-20 Chem Think Technical Press CBC UofA
Chemical Thinking Lab Assignment 9 v1.2 | 2 Problem 2 (9p). Using only the MS and FT-IR spectra of Unknown B determine the molecular structure of Unknown B . Clearly justify your structure using the available data. Your analysis must include the MS and FT-IR data. To receive credit, you must respond with well written, very legible, complete sentences that correctly employs chemical terminology and concepts. Mass Molecular ion M+ 60 CH3 CH2 CH2 OH m/z 31 +CH2OH Propanol m/z 15 CH3 m/z 59 +CH2CH2CH2OH IR ---- 3400 cm^-1 O-H str 2996 cm^-1 C-H str 2924 cm^-1 C-H str 1050 cm^-1 C-O str (for 1 alcohol) Molecular formula C3H8O CHEM 151 LA 9 v1.2 MY © 2020 10-16-20 Chem Think Technical Press CBC UofA
Chemical Thinking Lab Assignment 9 v1.2 | 3 Problem 3 (9p). Using only the MS and FT-IR spectra of Unknown C determine the molecular structure of Unknown C . Clearly justify your structure using the available data. Your analysis must include the MS and FT-IR data. To receive credit, you must respond with well written, very legible, complete sentences that correctly employs chemical terminology and concepts. From the IR- The broad peak starting from about 3400 to 2400 cm-1 confirms that the compound is a carboxylic acid. It is a characteristic peak for carboxylic acid. Also the sharp peak at 1700 and at about 1300 cm-1 are for C=O and C-O stretching vibration respectively. From mass- Here, the intense peak at m/z = 60 is the molecular ion peak. So the compound is ethanoic acid. The fragmentation pattern are shown below- The peak at m/z = 43 is the base peak having the highest intensity. CHEM 151 LA 9 v1.2 MY © 2020 10-16-20 Chem Think Technical Press CBC UofA
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