Lab1 Recitation
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Transcript of Lab1 Recitation
Key Point Summaries• Start with lab lecture notes! Then compare to
procedure/results• Practice good scientific writing• Full sentences (try), no first person, active voice, and
concise writing• “It was determined that Standard II, which had an Rf value
of 0.5, was a polar molecule because of its carboxylic acid group” vs. “Standard II (Rf = 0.5) is polar because of its carboxylic acid group”
• One page text maximum, but …• Can have appendix for ChemBioDraw graphics (1 pg max)
label as Figure 1, Table 2, Mechanism 2, Reaction 5, etc…
Recitations
• What will they be? • Real-life examples and applications of theory we learned
in lecture and applied in controlled settings in lab. • May help with post-lab quiz questions
• What will they not be? • Your key point summaries in spoken form.
• Hi, group 2 spies!• Mandatory
• Yay!
HPLC
• High performance liquid chromatography• Accurate
• Better reproducibility• Higher sensitivity (for smaller samples)
• Informative• Multiple detection techniques could follow (UV/Vis, mass
spectrometry)• Convenient
• Automatic
Image Source: http://web.nmsu.edu/~kburke/Instrumentation/Agilent_HPLC.gif
HPLC
Image Source: http://www.forumsci.co.il/HPLC/WEB-Pharm_Review/alkylphenones.gifhttps://sweepingthegarden.files.wordpress.com/2013/03/spongebob.jpghttp://www.extremescience.com/images/sailfish.jpghttps://s-media-cache-ak0.pinimg.com/736x/e7/b4/cc/e7b4cc5b29da05ef80bd8b395b940bab.jpg
Less polar More polar
Time
HPLC• High performance liquid chromatography• Accurate
• Better reproducibility• Higher sensitivity (for smaller samples)
• Informative• Multiple detection techniques could follow (UV/Vis, mass
spectrometry)• Convenient
• Automatic
Image Source: http://web.nmsu.edu/~kburke/Instrumentation/Agilent_HPLC.gif
TLC before HPLC
• HPLC (high performance liquid chromatography)• Quantitative, accurate, smart• But machine column can be difficult to clean out ($)
• Not disposable• AND need lots of solvent for longer time and labor ($$$)
• TLC• Easy set-up/disposable• Cost effective• Low sensitivity but suitable for normal use
Image Source: http://web.nmsu.edu/~kburke/Instrumentation/Agilent_HPLC.gif
Column Chromatography• Stationary: Gel (usually polar)• Mobile: Liquid (usually not as polar)• Good for clean up (before HPLC) as well as simple separation• Sample: Mixed compounds• Red: polar • Blue: not as polar
If all else fails…
• Separate using other techniques• Distillation (next week)• Extraction (the week after)• Crystallization (Chem 2321)
Food for thought
• Results (high to low Rf): • Ibuprofen• Aspirin• Phenacetin• Acetaminophen• Caffeine
• Can look at structure to justify results• Rf is related to polarity, and polarity is related to
structure.
Most to least polar
HO
O
1. Caffeine 2. Acetaminophen3. Phenacetin
4. Aspirin 5. Ibuprofen
N
N
N
N
O
O
Caffeine (most polar, lowest Rf)• Dipole-dipoles from inductive withdrawal and
resonance• Nitrogen and Oxygen can act as H-bond acceptor
N
N
N
N
O
O
Ibuprofen (least polar, highest Rf)• Has H-bond (polar), but has a really large nonpolar
group• Compare to other molecules
Hydrocarbon regionHO
O