8/7/2019 Finalexam review Ochem Lab1

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Chem. 2612 Org Chem I Lab Review Material for Final Exam Scheduled During your Lab Lecture W, Nov. 24, 1 PM in SB2.03.12 (or M, Nov. 22, 5:30 PM in SB2.01.12) which will focusprimarily on experiments 6-12:

Substitution reactions:

VI. SN2 process: n-butyl bromide + Na+- O2CCH3 n- butyl acetate + Br-

Concepts: RBr reaction run in neutral media to allow good nucleophile, acetate, to attack primaryalkyl halide directly. Role of aprotic, polar solvent (DMF) in SN2 processes.

VII. SN1 process: t-pentanol + HCl t-pentyl Cl) + H2OConcepts: ROH reaction run in acid to produce ROH2

+ and provide a better leaving group (H2O);SN1 vs SN2 mechanism; AgNO3 & NaI tests:

acetoneRX + AgNO3 R

+ NO3- + AgX (ppt) is SN1 rx: 3

o > 2o> 1o; RX + NaI R-I + NaX (ppt) is SN2 rx: 1o > 2o> 3o

Practical: Use of acids to protonate alcohols, difference in reaction conditions for the tworeactions; reflux reaction for SN2, use of base extraction to remove traces of acid from reactionmedium before product isolation; distillation vs co-distilllation (with water); use of drying agents(anhydrous sodium sulfate); observations during AgNO3 & NaI tests on RX: formation of AgX or RBror RCl ppt respectively as in above equations;product yield determinations; IR purity check should lose O-H @3300 cm-1 & C-O @1000-1200 cm-1of alcohol

VIII. Kinetics of t-pentyl chloride solvolysis

Concepts: solvolysis (solvent acts as nucleophile in substitution reaction); kinetic analysis: 1st

order vs 2nd order tells which reactants are involved in rate-determining step; SN1 involves onlysubstrate which dissociates into carbocation, then reacts rapidly with nucleophile; effect of solventpolarity on rate of this SN1 reaction; concept of titration

Practical: titration process; indicator, why a blank is run; how to determine molar concentration ofHCl (and consequently how much RCl is left) in aliquots pulled at different time intervals; determining

rate constant, k, for reaction

IX. Dehydration of cyclohexanol to cylcohexene (brief review)

Concepts: elimination reaction, probable E1 scheme with carbocation intermediate, which loses aproton from a neighboring carbon atom; Tests for unsaturation decolorization of bromine (whichadds to - bond to produce dibromoalkane) or color change with permanganate (which also adds)

Practical: Co-distillation of cyclohexene with water (lower BP than either pure compound);observations during unsaturation tests above; IR of alkene (C=C @ 1600 cm-1) vs alcohol (O-H@3300 cm-1 & C-O @1000-1200 cm-1)

X. Bromination of trans-cinnamic acid

Concepts: addition reaction bromonium ion intermediate; stereoselective anti-addition whichproduces only some rather than all possible stereoisomers; stereogenic centers, molecules with 2stereogenic centers enantiomers (same properties) versus diastereomers (different properties)

Practical: observations during reaction as cinnamic acid dissolves, red Br2 color goes away,product precipitates; mp determination; IR characteristics of R-CO2H (very broad O-H @3300 -2500cm-1, C=O @ 1720 cm-1 & C-O @1000-1200 cm-1); MP determination

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8/7/2019 Finalexam review Ochem Lab1

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XI & XII. NMR spectroscopy

Concepts Magnetic properties of H; the NMR experiment absorption of RF to cause nuclearspin inversion; shielding and deshielding effects of nearby - and - electrons on effective magneticfield felt by Hs in organic molecules, use of TMS as reference; NMR information: # of signals tellshow many different types of H in a molecule; chemical shift (ppm) tells what type of H (especially C-H) is present; intensity (integral) of signals tells relative amounts of each type of H; & splitting patterntells about neighboring Hs and molecule framework; only neighboring, non-equivalent C-Hs couple& N neighboring Hs will split a signal into N + 1 peaks; be able to distinguish between equivalent &non-equivalent Hs in chemical structures

Practical: sample preparation, placing tube in probe; interpretation of NMR; being able to usetables to assign or predict chemical shifts for various Hs in a molecule; understanding simple splittingpatterns & what they indicate

V-XII. Electromagnetic spectrum; Infrared spectroscopy

Concepts: electromagnetic spectrum, wave properties of light, wavelength & relationship toenergy, Spectroscopy interaction of light energy with molecules; electronic excitation caused byUV-visible light, vibrational excitation by IR light; vibrational properties of chemical bonds; use of IR

as a method of detecting bonds and functional groups, and structure confirmation by fingerprinting.

Optional Help session will be scheduled for Mon, 11/22 @ 1PM in SB 2.03.12 and/or Sun,11/21 or Tues, 11/23 (late afternoons) TBA. The session will deal primarily with the practiceexam & NMR and structure determination by IR-NMR spectroscopy.

The exam format will include Multiple Choice, drawing product structures & simple mechanismsand short answer questions (sample exam is posted on WebCT). Bring a par-score opscan form.