1. in the proton NMR spectrum of a secondary amide, the amideproton\'s signal is
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1. in the proton NMR spectrum of a secondary amide, the amideproton's signal is: a. sharp, around 5.0 (ppm) b. sharp, around 10.0 (ppm) c. broad, around 9.0 (ppm) d. broad, around 7.0 (ppm) e. usually not observed 2. The chemical shifts for protons to a carbonylgroup: a. are similar for all acid derivatives b. are farthest downfield for carboxylic acids c. are farther downfield than those to a nitrile d. fall between 3.1 and 4.2 (ppm) e. fall between 1.3 and 1.8 (ppm) 3. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for amides is about? a. 1700 cm -1 b. 1735 cm -1 c. 1800 cm -1 d. 1660 cm -1 e. 2200 cm -1 4. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for acid chlorides is about: a. 1700 cm -1 b. 1735 cm -1 c. 1800 cm -1 d. 1660 cm -1 e. 2200 cm -1 5. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for esters is about: a. 1660 cm -1 b. 1700 cm -1 c. 1735 cm -1 d. 1800 cm -1 e. 2200 cm -1 6. In the mass spectrum of pantanoic acid, the base peakoccurs at m/z: a. 102 b. 101 c. 85 d. 73 e. 60 7. in the propanoate ion: a. both the carbon-oxygen bonds are the same length b. the carbon-oxygen double bond is shorter c. the carbon- oxygen double bond is longer d. one of the oxygen atoms bears a -1 charge e. the carbon atom bears a -1 charge 8. the common name for pentanedioic acid is : a. pimelic acid b. oxalic acid c. glutaric acid d. succinic acid e. adipic acid 9. The combination of a carbonyl group and a hydroxyl group onthe same carbon atom is called a _______ group. a. carbamate b. carbonate c. urethane d. carboxyl e. carboxylate 1. in the proton NMR spectrum of a secondary amide, the amideproton's signal is: a. sharp, around 5.0 (ppm) b. sharp, around 10.0 (ppm) c. broad, around 9.0 (ppm) d. broad, around 7.0 (ppm) e. usually not observed 2. The chemical shifts for protons to a carbonylgroup: a. are similar for all acid derivatives b. are farthest downfield for carboxylic acids c. are farther downfield than those to a nitrile d. fall between 3.1 and 4.2 (ppm) e. fall between 1.3 and 1.8 (ppm) 3. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for amides is about? a. 1700 cm -1 b. 1735 cm -1 c. 1800 cm -1 d. 1660 cm -1 e. 2200 cm -1 4. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for acid chlorides is about: a. 1700 cm -1 b. 1735 cm -1 c. 1800 cm -1 d. 1660 cm -1 e. 2200 cm -1 a. 1700 cm -1 b. 1735 cm -1 c. 1800 cm -1 d. 1660 cm -1 e. 2200 cm -1 5. While the carbonyl stretching frequency for simplealdehydes, ketones, and carboxylic acids is about 1710 cm -1, thecarbonyl stretching frequency for esters is about: a. 1660 cm -1 b. 1700 cm -1 c. 1735 cm -1 d. 1800 cm -1 e. 2200 cm -1 6. In the mass spectrum of pantanoic acid, the base peakoccurs at m/z: a. 102 b. 101 c. 85 d. 73 e. 60 7. in the propanoate ion: a. both the carbon-oxygen bonds are the same length b. the carbon-oxygen double bond is shorter c. the carbon- oxygen double bond is longer d. one of the oxygen atoms bears a -1 charge e. the carbon atom bears a -1 charge 8. the common name for pentanedioic acid is : a. pimelic acid b. oxalic acid c. glutaric acid d. succinic acid e. adipic acid 9. The combination of a carbonyl group and a hydroxyl group onthe same carbon atom is called a _______ group. a. carbamate b. carbonate c. urethane d. carboxyl e. carboxylateExplanation / Answer
1. Secondary Amide: ---R-C(=O)-NHR'--- Amides have broadened signals due to a 'quadrupole moment' effect.A nitrogen (14N) nucleus has a spin (I) of 1, as opposedto 15N, 13C and 1H, which have I =1/2. The high 'I' value means that the charge distribution on thenucleus is non-symmetrical, and this affects the relaxationmechanism of the nucleus during NMR, resulting in a broadenedsignal. Long story short: this rules out (a), (b) and (e). I wasn't able tofind it in my data tables, but I think secondary amides resonatecloser to 7 ppm than 9 ppm (I looked up the NMR data forN-methylformamide (HC(=O)NHCH3), in which the amideproton resonates at 7.4 ppm). I would pick (d). 2. Not sure about this one! Alpha to carbonyl group: --R-C(=O)-C(H)--- First of all, rule out (e) - this is waaay to low for a proton nextto a carbonyl. Looking at my data tables, I'm also inclined tobelieve that 3.1-4.2 ppm (d), is too high. Alpha to a nitrile: --C(H)-C=N; resonatesat 2.3-2.7 ppm Carboxylic acids: --C(H)-COOR; resonates at ~2.2-2.5 ppm (I think?) Downfield = High ppm, so I would rule out (b), since the nitrilerange is higher than the carboxylic acid range (assuming my data iscorrect!). This leaves (a) and (c). Disregarding aromatics(e.g. CH-CO-Ar @ 3.3 ppm), I can't see any carbonyl compounds whichresonate >2.7 ppm on my data table (this doesn't mean they don'texist!), so I would probably pick (a). 3. I would pick (d) 1660 cm-1. (I'm assuming you havedata tables...) 4. Acid chloride: --C=O-Cl. Strectch range ~1750-1820cm-1. I'd probably pick (c) 1800 cm-1, asthis value is in the middle (-ish) of that range. 5. Ester: -R-C=O-O-R'-. Depending on the nature of the ester, Iwould suggest a range of 1735-1750 cm-1 for saturatedesters. So option (c). 6. Pentanoic acid:CH3-CH2-CH2-CH2-COOH I admit I looked this one up. The base peak (= highest peak) is at60 m/z = (e). Note that the base peak does not (neccessarily) occurat the molecular weight of the molecule (that's the molecular ion,in most cases). 7. Propanoate ion:CH3-CH2-COO- Rule out (e): the carbon atom is uncharged. The propanoate ion exists as a resonance-stabilised structure (thecharge is 'delocalized' over both of the oxygen atoms), similar tothe way the nitro (NO2) group resonates. This means bothof the C-O bonds are the same length, and this length is between adouble and single bond length. I would pick (a). 8. Dioic = two acid groups, so pentanedioic acid:HOOC-CH2-CH2-CH2-COOH. This isotherwise known as glutaric acid - or so my friend Wikipedia tellsme... =P 9. Carbonyl + hydroxyl -> C=O + OH -> C=O(OH) ->carboxyl. Carboxyl = COOH, whereas carboxylate is the salt,COO- Carbamate = Urethane = R-O-C=O-NR'R''; has N, soobviously not that one! Carbonate = CO3-; has too many O's!
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