lab1 recitation

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Lab 1 Recitation Thin-Layer Chromatography

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TLC

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Lab 1 RecitationThin-Layer Chromatography

Key Point Summaries

• Grading!!!

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

Acetaminophen, Phenacetin• Between the two, Acetaminophen has 1 more H-

bond donor (more polar)

Aspirin

• Easily formed intramolecular H-bonding limits Aspirin’s ability to bond intermolecularly