351 MT Fall 2025
Here is an post-mortem analysis / "how to" for the MT. The questions are split by the sections. At the start of each section are a few suggestions of what to look for or how to tackle the question type.
| Qu1: | All the bonds indicated are CC bonds. We have C=C and 2 C-C. One C-C is sp2C-sp3C then other is sp3C-sp3C. The increased s character of sp2 makes that bond stronger (v1=A, v2=D) |
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| Qu 2: | Ranking resonance structures...we need to check for complete octets and maximised bonding (within the octet rule limitations) and then for charge separation in accord with electronegativity. (v1=AB, v2=AB) |
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| Qu 3: | Basicity...Think about the availability of the electrons in the bases, always a good idea to draw in the lone pairs because lone pairs are more available than bonded pairs. We have N systems. +ve N does not have a lone pair only bonded pairs, so it's not very basic. In the neutral N systems, one N is sp3 the other sp. A lone pair in an sp hybrid orbital has greater s character and is closer to the +ve nucleus which makes it less available than an sp3 N. (v1=C, v2=E) |
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Qu 4: |
The syn eclipsed conformation is highest energy (proximity of the larger methyl groups), then gauche and anti is lowest energy (most stable). (v1=A, v2=E) | |
| Qu 5: | Radical stability of this set is affected by (i) degree of substituion and (ii) resonance. From most stable to least stable we have secondary allylic > primary allylic > primary (v1=A, v2=C) |
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| Qu 6: | Each different monochlorination product comes from a different type of H in pentane. We can do the calculations considering the number of H of each type and the relative rectivity of each position. For the 1-chloro isomer, it would be 6x1, for 2-chloro 4 x 3.9 and 3 chloro = 2 x 3.9 so % 2-chloropentane > % 3-chloropentane > % 1-chloropentane. (v1=D, v2=C) |
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| Qu 7: | Acidity...the structures are an amine NH, CH adjacent to a carbonyl in a ketone and a CH of a methy group on an internal alkyne. |
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| Qu 8: | Acidity... If the pH is more basic than the pKa, then the proton will have been removed to form the conjugate base. So at pH 2.5, the carboxylic acid is deprotonated by the ammmonium center is not. Since amines are basic, R-NH2 can't exist in the presence of RCO2H. (v1=C, v2=D) | |
MOLECULAR PROPERTIES: |
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| Qu9: | Acidity...the most acidic functional group in the molecule is the phenol (typical pKa = 10) an -OH system with some resonance stabilistion of the conjugate base. (v1=A, v2=D) |
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| Qu10: | O11 is part of a ketone so the lone pairs are in sp2 hybrid orbitals and N21 is a non-conjugated amine where the lone pair is in an sp3 hybrid orbital. (v1=B, v2=D) | |
| Qu11: | O1 is part of a phenol where the O lone pairs interact with the adjacent pi system so the O is sp2 and C14 is part of a simple alkene so it is also sp2. (v1=D, v2=A) |
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| Qu12: | IHD = pi + r so there are 5 rings and 5 double bonds : 5 + 5 = 10 (v1= D, v2= B) | |
| Qu13: | N21 = is part of an amine, O8 is part of a ether (v1= AE, v2= BD) |
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| Qu14: | The chirality center at C9 (where there are 4 different groups attached to the sp3 C) and it has the R configuration (O > C(OOC) > C(CCC) > H). Remember that the low priority group has to be away when determining the sense of rotation. The C23=C24 is terminal (=Ch2) and therefore does not have stereochemistry. (v1= E, v2= E). |
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| Qu15: | All are CC bonds, so the double bond will be the shortest, C23=C24 (v1= E, v2= E). | |
| Qu16: | The mosty basic site is the amine N21 and amines (pKa = 10) will be fully protonated with 1 eq of HCl (pKa = -7) (v1= AB, v2= E). | |
| Qu17: | C22 is a primary allylic center (v1= AC, v2= AD). | |
SPECTROSCOPY: |
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| Qu18: | The IR does not show a C=O near 1700 cm-1 but it does show a strong, broad band at 3350 cm-1 (O-H). Given the absence of the C=O, it can't be the carboxylic acid, so it must be the alcohol. (v1=A, v2=D) | |
| Qu19: | The IR shows a strong C=O near 1720 cm-1 (which woul d be about normal for a simple ketone), no -OH above 3000 cm-1. Careful inspection does not suggest C-O at about 1200-1100 cm-1 (therefore not an ester), supporting the ketone. (v1=D, v2=B) | |
| Qu20: | The IR shows a strong C=O near 1735 cm-1 (which would be highl for a simple ketone), no -OH above 3000 cm-1. Careful inspection suggests C-O at about 1250 and 1050 cm-1 supporting the ester. (v1=E, v2=C) |
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| Qu21: | The IR does not shows a C=O near 1700 cm-1. The IR shows a medium double band near 3500-3350 cm-1 that could be an -NH2. On closer inspection, the C-H stretches are > 3000 cm-1 indicating sp2 C-H only and there are possible aromatic C=C near 1600 and 1500cm-1.. This would be consistent with the aromatic primary amine. (v1=AE, v2=BC) |
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| Qu22: | The IR shows a strong double C=O near 1810 and 1750cm-1 (which would be very high for a simple ketone, probably an anhydride), no -OH above 3000 cm-1. This would be consistent with acyl anhydride. (v1=C, v2=A) |
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| Qu23: | The IR does not show a C=O near 1700 cm-1. The IR does show an strong band around 3300 cm-1 and a medium sharp band near 2200cm-1 for a triple bond. The 3300cm-1 band would be consistent with a terminal alkyne. (v1=AB, v2=AB) | |
NOMENCLATURE: |
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| Qu24: | The longest chain is C8 so an octane. There are two substituents, an ethyl group and the t-butyl or 1,1-dimethylethyl group. Since the alphabetical order is wrong for the t-butyl group, we need to need the complex version and alphabetise it based on the "d" (first letter in the brackets). The first point of difference does not resolve the numbering so it is dictated by the alphabetical order. Therefore for we 4-(1,1-dimethylethyl)-5-ethyloctane (v1=C, v2=C) |
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| Qu25: | If named as a nitrile, then the alkene would be C2, so need to name as a cyano substituent. The longest chain including the principal functional group (an alkene) is C6, so we have a hexene system. The C=C is at C3, with the cyano group at C3. The alkene has Z stereochemistry since the CN is higher priority than the ethyl group at C3. Therefore we have (Z)-3-cyanohex-3-ene (v1= D, v2= C) | |
| Qu26: | A substituted cyclohexene. Need to number to make the alkene C1 & C2. In this case, the first point of difference rule dictates needing to give the methyl group the lower number and then need to list the substituents alphabetically (ethyl before methyl) ignoring the di prefix. Hence 5-ethyl-1-methylcyclohex-1-ene. (v1=E, v2=E) |
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| Qu27: | The longest chain including the principal functional group (a ketone) is C6, so we have a hexenone system. The C=O is the higher priority functional group and gets the lower number of C3 with the trans stereochemistry double bond at C4-C5 and a methyl group at C4. Therefore we have trans-4-methylhex-4-en-3-one (v1= E, v2= B) |
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| Qu28: | Naming of simple alkyl groups : here we save an sec-butyl (v1 = D, v2 = C) |
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| Qu29: | Substituted benzenes and ester naming. The C=O (acid) side of the ester is based on benzoic acid. The ortho methyl group needs to be on the ArC next to the C=O on the acid side of the ester and then an ethyl group on the alcohol side of the ester N (v1 = D, v2 = E) |
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| Qu30: | R/S stereochemistry |
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| Qu31: | The bicyclic system needs to have 8C (oct) and an alkene since it is an octene. The [3.2.1] indicates the number of C atoms in each link between the central C atom. Need to start to number from the bridgehead C then round the larger ring first with the alkene adjacent to the bridgehead. (v1 = D, v2 = C) |
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