Carbon Proton Part quaternary carbon quaternary carbon quaternary carbon Alkene CH

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Benedict Logan Hudson
7 years ago
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1 1) 13C and SQC give the below parts Carbon Proton Part quaternary carbon quaternary carbon quaternary carbon 7.15 Alkene C Alkene C Alkene C C C C3 2. MF = C1013 = = 17 missing an, which is verified by the broad singlet at 4.8 ppm in the NMR C1014 = Unsat = = 4 Given that there are 6 carbons in the range and the 3 protons in the aromatic range ( NMR) there must be an aromatic ring. This satisfies the Unsat of The aromatic ring is trisubstituted and given the coupling of two doublets and a singlet must be a 1,2,5-trisub. The other parts, from NMR, are a Me singlet and an isopropyl group (the two Methyl groups are doublets and the C at 3.2 is a septet), and the to give: C 3 C 3 C C 3 Thus, these three pieces need to be placed on the 3 available spots of the ring and the MBC will direct their placement. I begin with simply sticking the on then deciding what to stick next to it. Using chemical shifts the carbon with the on it must be the 1

2 152 resonance. Looking at the C proton at 3.2 (in red) 4 correlations are observed from it, a correlation to the isopropyl methyl groups ( 2 J), to an aromatic C carbon at, and two quaternary peaks - at 152 and 131. Thus, the below appears correct and leads to the right structure. Since the isopropyl methyl protons at 1.3 show a correlation into 131 the assignments shown must be correct, i.e. this correlation can only be a 3- bond connectivity. Me Me 3 C C C 3 If the above is correct then the protons on the isolated methyl (in red below) should show 3 correlations to 2 aromatic C carbons and 1 quat aromatic carbon. This is observed and allows assignment of the 136 resonance. The remaining two carbons are already assigned using SQC, i.e. the proton that is a singlet in the NMR is attached to 116 and thus 121 must be the remaining. C 3 C C C C 3 C 121 The mass spec is simply fragmentation of a Me group to give a benzylic cation. C 3 C 3 C 3 3 C 3 C 135 2

3 2) Parts from SQC J Nat Prod 2011, 1787 Proton Carbon XC 3 C C C13142 = = 32 missing two oxygens to give C13144 = /2(14) + 1 = 7 The above parts of 8 alkene carbons leads to a total of 4 alkenes, plus two carbonyls leaving one ring. 4. A few modifications can initially be made based on the Mass Spec (43 ion) and NMR (resonances and 6.7 J = 16 z. Both a trans alkene and an acyl group are are present. A methoxy group is present and one of the carbonyls is an ester (I have assigned this to 171, but 163 or 158 could also be the ester carbon). 3

4 3 C C C ring Using the MBC and starting at the Methyl of the acyl group the connectivity can be established. The methyl at 2.23 is connected to the ketone at 199, which also show a correlation to the proton at a singlet. The proton also shows a correlation into the carbon at 32, which is a 3-bond connectivity so the below is correct. (There may also be a correlation of C131 into 2.23 but it is difficult to tell). SQC illustrated that is connected to C Proton has a total of 4 correlations, one into the carbonyl carbon at 199 and 32 (both are established connections), the Me carbon at 13 and the C at 138 ppm. These must be 3-bond connections and the 2-bond is missing, otherwise we run out of points of attachment. Since the alkene carbon of 138 is attached to, see above parts, the following pathway is established: The missing quat. carbon can be found by following the correlations from the protons on the Me group at It appears to show 3 peaks connecting 131 and 138, which are 3-bonds. The 3rd correlation is to the resonance at, which is a quat alkene, and must be a 2 bond. 3 C C missing C 3 3 C C 3 4

5 Looking at proton it shows a correlation to the methyl carbon at and 131 both of which are 3 -bond and verifies the current fragment. It also has a correlation to the 158 carbon, a quaternary alkene, which also would have to be a 3-bond (since we know that carbons 138 and are connected). This gives below left. The 158 carbon has correlations back to proton, a 2-bond and confirms, plus to the proton at 6.26, which is connected to carbon 103.8, giving: C C 103 C 3 C Looking at the correlations from proton 6.26, we can see the connectivity to back to carbons and 158, but two more exist that show connectivity to 171 and 90. These must represent both a 2- and 3-bond connectivity, but which is which must be resolved. The carbon at 171 has 3 correlations - to protons 6.26 (established) and to 5.57 and the methoxy at Initially, you could draw the below left based on the chemical shift of 171 and the correlation to the methoxy. owever, there is no way to make another connection to the proton at 5.57 unless carbon 171 is actually an alkene. Furthermore, there appears to be small, long-range coupling between protons 5.57 and 6.26, which would represent a 4 J coupling. Thus, the structure on the right looks better. 3 C C Me C C Me 3.89 This leaves only a an ester and a ring to incorporate and the below structure satisfies this: 163 C 3 5

6 Confirmation of this molecule is as follows: an alpha fragmentation produces the 43 ion and the loss of the side chain confirms the ring. C 3 43 C 3 C C 3 The high UV can be rationalized by the extended conjugation in which the base is the ketone. The actual is ! base ketone 90! extended conjugation 31! alkyl at beta position 12! Beta alkyl 348! The IR stretches of 1678 does fit an unsaturated ketone and the 1760 a lactone. Finally, the stereochemistry of one alkene was established via a J coupling of 16 z, however the alpha, beta alkene next to the ketone must be established via the NESY. The double-headed arrows in red indicate the NE s that are observed in the NESY and not only help confirm the structure but also the stereochemistry. C C 3 6

IR Applied to Isomer Analysis

DiscovIR-LC TM Application Note 025 April 2008 Deposition and Detection System IR Applied to Isomer Analysis Infrared spectra provide valuable information about local configurations of atoms in molecules.