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The polymer polylactic acid, PLA, shown above, is used to make soluble stitches which are absorbed by the body following surgery - VCE - SSCE Chemistry - Question 4 - 2009 - Paper 1
Question 4
The polymer polylactic acid, PLA, shown above, is used to make soluble stitches which are absorbed by the body following surgery. Other than the peak given by the T... show full transcript
Worked Solution & Example Answer:The polymer polylactic acid, PLA, shown above, is used to make soluble stitches which are absorbed by the body following surgery - VCE - SSCE Chemistry - Question 4 - 2009 - Paper 1
Step 1
one set of peaks in the 'H NMR
Answer
The structure of polylactic acid (PLA) consists of repeating units based on lactic acid. The monomeric unit, lactic acid, provides a unique spectral fingerprint in NMR. However, due to the symmetry in the PLA polymer, it results in only one set of peaks for the hydrogen atoms in the NMR spectrum. Thus, this option does not apply.
Step 2
two sets of peaks in the 'H NMR
Answer
This option suggests the presence of two distinct environments for the hydrogen atoms. Given PLA's structure, this is not the case since the hydrogens adjacent to the ester linkages and methyl groups do not create two separate environments in a notable manner.
Step 3
Step 4
four sets of peaks in the 'H NMR
Answer
Considering the symmetrical nature of PLA, it's important to note that four distinct sets of peaks representing different hydrogen environments do not exist in this structure due to the repeating unit's consistency. The polymer effectively simplifies the NMR signal.