Cinnamaldehyde is the primary organic molecule that gives cinnamon its characteristic scent and zest. This compound is composed of a monosubstituted benzene ring, a trans-alkene, and an aldehyde functional group. The molecular formula and molecular weight of cinnamaldehyde is C 9 H 8 O and 132.16g/mol, respectively. The structure of cinnamaldehyde is shown in Figure 1. 1 H 1D NMR Spectrum appearing at 9.73 ppm. The chemical shift of HA is indicative of the aldehyde proton at C1. Figure 3 is an expanded view of the aromatic and alkene region gHMQC NMR Spectrum 13 C 1D NMR Spectrum The 13 C spectrum of cinnamaldehyde is shown in Figure 6. The spectrum was recorded at 500 MHz ( 1 H) with a a spectral width of 28409.1 Hz. Resonance CA, the most downfield resonance, belongs to C1, the carbonyl carbon. The three peaks at 77.3 belong to the solvent, CDCl 3 . Figure 7 represents the aromatic region between 127 ppm and 153 ppm. This also includes the alkene carbons that are part of the conjugated system. References HanHong. Trans-Cinnamaldehyde. Web. 20 September 2015. <http://www.hanhonggroup.com/nmr/nmr_en/B34317.html> Claridge, Timothy D. W. High-Resolution NMR Techniques in Organic Chemistry. Amsterdam: Elsevier, 2009. Spectral Database for Organic Compounds SDBS. National Institute of Advanced Industrial Science and Technology (AIST). Japan. Web. 20 September 2015. <http://sdbs.db.aist.go.jp/sdbs/cgi-bin/ENTRANCE.cgi> Since all of the proton assignments have been made, a 2- Dimensional gHMQC will help resolve the peaks that pertain to the aromatic/alkene region. The gHMQC spectrum was recorded at 500 MHz ( 1 H) with a spectral width of 6038.65 Hz in the direct dimension and 28409.1 Hz in the indirect dimension. Figure 8 and 9 show the NOESY NMR Spectrum The two remaining unresolved aromatic protons will be deciphered using a gCOSY experiment. Figure 5 represents the aromatic region of a gCOSY spectrum that was recorded at 500 MHz ( 1 H) with a spectral width of 6038.65 Hz and 1024 complex points. We’ll start by inspecting the cross peak resonance that belongs to H5/H9. H5/H9, resonance HB, is only coupled to H6/H8; Thus, H6/H8 is resonance HD. By deduction we are able to assign resonance HE to H7. However, the gCOSY also shows that resonances HE and HD are coupled to each other providing further evidence. All of the protons have been assigned 13 C DEPT NMR 1D Spectrum The 13 C DEPT spectrum was recorded at 500 MHz with a spectral width of 28409.1 Hz and a relax delay of 5s. The 13 C DEPT shows the hybridization of the carbons pertaining to cinnamaldehyde. All but one carbon is sp2 hybridized, tertiary carbons. We can assign resonance CC to atomic position C4 located at 134 ppm. Results By careful analysis of the 1D and 2D spectra of all of the protons and carbons have been assigned. We were able to assign some protons directly based on the fine structure of the 1 H-1D spectrum. The assignment ambiguities were resolved using the NOESY and gCOSY experiments. Based on the assigned protons, assignment of the directly bound carbons was carried out using a gHMQC experiment. The DEPT, which provides derived sub-spectral analysis of the 1D- 13 C spectrum, provided key confirmation of resonance assignments. The 1 H 1D NMR spectrum of cinnamaldehyde is shown in Figure 2. The spectrum data was recorded at 500 MHz ( 1 H) with a spectral width of 6038.65 Hz and 8192 complex points. The solvent peak (CDCl 3 ) appears at 7.27 ppm. Resonance HA is the most downfield doublet 1 H NMR Assignments (ppm) H1 9.73 H2 6.74 H3 7.48 H5/H9 7.58 H6/H8 7.46 H7 7.45 The molecule has two alkene protons that are trans to each other. In order to distinguish between the two, splitting patterns were 13C NMR Assignments (ppm) C1 193.75 C2 131.30 C3 152.82 C4 134.01 C5 129.13 C6 128.62 C7 128.52 direct associations between the proton and carbon nuclei. Consequently, CG correlates with H5/H9 and is therefore C5. CB correlates with H3 and is therefore C3, leading to CD being C2, CE being C6/C8, and CF being C7. By The remaining alkene proton, HC, is assigned to H3, a doublet (J=15.974Hz) found at 7.48 ppm. The aromatic region has a line of symmetry running through the carbons labeled 4 and 7, giving rise to three unique aromatic proton and carbon resonances. In this molecule, C5 and C9, C6 and C8, are considered to be chemically equivalent. Definitive assignment of the remaining protons requires 2D NMR experimentation in order to resolve the remaining three protons. gCOSY NMR Spectrum Figure 4 shows the aromatic/alkene region of a NOESY experiment. The NOESY was ran at 500 MHz ( 1 H) with a spectral width of 6038.65 Hz and a MixN time of 500ms. The completely conjugated structure of cinnamaldehyde gives some rigidity to the molecule and places H5 and H2, resonance HF, close enough to experience the Nuclear Overhauser Effect, NOE. By inspecting the crosspeaks, it is observed that H2 is only coupled to resonance HB. Therefore, resonance HB, the doublet, belongs to H5/H9. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 10 process of elimination, we can go ahead and assign peak CC to C4. Confirmation of these assignments is accomplished by careful consideration of the results of the DEPT experiment, Figure 10. Figure 9 used. H3 would be split into a doublet by the proton bound to C2, whereas H2 would be split into a doublet of doublets due to the presence of the two surrounding nonequivalent protons at C3 and C1. Resonance F at 6.74 ppm is a doublet of doublets (15.732 Hz, 7.538 Hz) and is assigned to H2.
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Cinnamaldehyde is theprimary organic moleculethat gives cinnamon itscharacteristic scent and zest.This compound iscomposed of amonosubstituted benzenering, a trans-alkene, and analdehyde functional group.
The molecular formula and molecular weight ofcinnamaldehyde is C9H8O and 132.16g/mol, respectively.The structure of cinnamaldehyde is shown in Figure 1.
1H 1D NMR Spectrum
appearing at9.73 ppm.The chemicalshift of HA isindicative ofthe aldehydeproton at C1.Figure 3 is anexpandedview of thearomatic andalkene region
gHMQC NMR Spectrum
13C 1D NMR SpectrumThe 13C spectrum ofcinnamaldehyde isshown in Figure 6.The spectrum wasrecorded at 500MHz (1H) with a aspectral width of28409.1 Hz.Resonance CA, themost downfieldresonance, belongsto C1, the carbonylcarbon. The threepeaks at 77.3 belongto the solvent,CDCl3. Figure 7represents thearomatic regionbetween 127 ppmand 153 ppm. Thisalso includes thealkene carbons thatare part of theconjugated system.
ReferencesHanHong. Trans-Cinnamaldehyde. Web. 20 September 2015.
<http://www.hanhonggroup.com/nmr/nmr_en/B34317.html>Claridge, Timothy D. W. High-Resolution NMR Techniques in Organic
Chemistry. Amsterdam: Elsevier, 2009.Spectral Database for Organic Compounds SDBS. National Institute
of Advanced Industrial Science and Technology (AIST). Japan. Web. 20September 2015. <http://sdbs.db.aist.go.jp/sdbs/cgi-bin/ENTRANCE.cgi>
Since all of the proton assignments have been made, a 2-Dimensional gHMQC will help resolve the peaks thatpertain to the aromatic/alkene region. The gHMQCspectrum was recorded at 500 MHz (1H) with a spectralwidth of 6038.65 Hz in the direct dimension and 28409.1Hz in the indirect dimension. Figure 8 and 9 show the
NOESY NMR Spectrum
The two remaining unresolved aromatic protons will bedeciphered using a gCOSY experiment. Figure 5 representsthe aromatic region of a gCOSY spectrum that was recordedat 500 MHz (1H) with a spectral width of 6038.65 Hz and 1024complex points. We’ll start by inspecting the cross peakresonance that belongs to H5/H9.H5/H9, resonanceHB, is only coupledto H6/H8; Thus,H6/H8 is resonanceHD. By deduction weare able to assignresonance HE to H7.However, the gCOSYalso shows thatresonances HE andHD are coupled toeach other providingfurther evidence. Allof the protons havebeen assigned
13C DEPT NMR 1D Spectrum
The 13C DEPT spectrum was recorded at 500 MHz with aspectral width of 28409.1 Hz and a relax delay of 5s. The13C DEPT shows the hybridization of the carbons pertainingto cinnamaldehyde. All but one carbon is sp2 hybridized,tertiary carbons. We can assign resonance CC to atomicposition C4 located at 134 ppm.
ResultsBy careful analysis of the 1D and 2D spectra of all of theprotons and carbons have been assigned. We were ableto assign some protons directly based on the fine structureof the 1H-1D spectrum. The assignment ambiguities wereresolved using the NOESY and gCOSY experiments. Basedon the assigned protons, assignment of the directly boundcarbons was carried out using a gHMQC experiment. TheDEPT, which provides derived sub-spectral analysis of the1D-13C spectrum, provided key confirmation of resonanceassignments.
The 1H 1D NMR spectrum of cinnamaldehyde is shownin Figure 2. The spectrum data was recorded at 500MHz (1H) with a spectral width of 6038.65 Hz and 8192complex points. The solvent peak (CDCl3) appears at7.27 ppm. Resonance HA is the most downfield doublet
1H NMRAssignments (ppm)
H1 9.73
H2 6.74
H3 7.48
H5/H9 7.58
H6/H8 7.46
H7 7.45
The moleculehas twoalkeneprotons thatare trans toeach other. Inorder todistinguishbetween thetwo, splittingpatterns were
13C NMR Assignments(ppm)
C1 193.75
C2 131.30
C3 152.82
C4 134.01
C5 129.13
C6 128.62
C7 128.52
direct associationsbetween the protonand carbon nuclei.Consequently, CGcorrelates with H5/H9and is therefore C5.CB correlates with H3and is therefore C3,leading to CD beingC2, CE being C6/C8,and CF being C7. By
The remaining alkene proton,HC, is assigned to H3, a doublet(J=15.974Hz) found at 7.48 ppm.The aromatic region has a line ofsymmetry running through thecarbons labeled 4 and 7, givingrise to three unique aromaticproton and carbon resonances.In this molecule, C5 and C9, C6and C8, are considered to bechemically equivalent. Definitiveassignment of the remainingprotons requires 2D NMRexperimentation in order toresolve the remaining threeprotons.
gCOSY NMR Spectrum
Figure 4 shows the aromatic/alkene region of a NOESYexperiment. The NOESY was ran at 500 MHz (1H) with aspectral width of 6038.65 Hz and a MixN time of 500ms. Thecompletely conjugatedstructure ofcinnamaldehyde givessome rigidity to themolecule and places H5and H2, resonance HF,close enough toexperience the NuclearOverhauser Effect, NOE.By inspecting thecrosspeaks, it is observedthat H2 is only coupled toresonance HB. Therefore,resonance HB, thedoublet, belongs toH5/H9.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 10
process of elimination,we can go ahead andassign peak CC to C4.Confirmation of theseassignments isaccomplished bycareful consideration ofthe results of the DEPTexperiment, Figure 10.
Figure 9
used. H3 would be split into a doublet by the protonbound to C2, whereas H2 would be split into a doubletof doublets due to the presence of the two surroundingnonequivalent protons at C3 and C1. Resonance F at6.74 ppm is a doublet of doublets (15.732 Hz, 7.538 Hz)and is assigned to H2.
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