Organic Lab Final

Front 1

Explain Distillation: (5)

Back 1

1. liquid molecules are in constant motion
2. molecules at surface escape into vapor phase and will do so until equilibrium is established
3. If temp increases, molecular motion, # molecules escaping and vapor pressure all increase
4. Tpressure=Vpressure+Lpressure+Apressure
5. When temp is reached where equilibrium vapor pressure of the sample=total pressure, evaporation increases and bubbles form and boils

Front 2

When to use simple distillation:

Back 2

-separation of components if thier boiling points differ by 40-50

Front 3

When to use fractional distillation:

Back 3

-liquid is composed of two volatile components, # molecules of x,y in a volume of vapor is proportional to their respective partial vapor pressures

Front 4

Using fractional distillation, explain how boiling points work:

Back 4

-liquid will have specific boiling point based on mole fraction of each component
-raoult's law, composition of vapor can be determined, relative to volatility
-the composition of vapor will be richer in more volatile species than the original mixture
-then vapor recondenses and the liquid now has a lower bp than the vapor
-vapor of second distillation is now even more rich in volatile species

Front 5

If the lower part of the distillation column is at a higher temperature than that of the top, some condensed vapor will revaporize....even as

Back 5

it flows down the column to return to the still-pot

Front 6

What should the ideal temperatures be?

Back 6

1. bottom of column: bp of less volatile component
2. at the top: bp of more volatile component

(there is a cycle where uncondensed and revaporized samples rise higher and cycle, each time making it richer in volatile)

Front 7

If entire column is same temp then: If bottom is too hot and top is too cool then:

Back 7

-no separation
-column will FLOOD with returning condensate

Front 8

Reflux Ratio:

Back 8

compares amount of condensate returning to pot vs. amount of vapor being collected

Front 9

Difference in BP to affect good separation should be no less than....

Back 9

20-30 degrees C

Front 10

In an ideal fractional separation:

Back 10

there should be two plateaus, first at the bp of more volatile and second at bp of less volatile, with very little volume separating the two

Front 11

What does Gas-Liquid Chromatography do?

Back 11

-partitions components of a mixture between a mobile gaseous phase and a stationary liquid phase

Front 12

What's the process in GL Chromatography?

Back 12

1. sample injected, immediately vaporized
2. vapor carried through column by flowing inert CARRIER GAS (he or n2) -the mobile phase
3. column is packed with solid support which is coated with viscous, high bp liquid-the stationary phase
4. as mobile phase moves, components continually partition between two

Front 13

What is Retention Time?

Back 13

1. elapsed time required for a component to move from injection point to detector
2. independent of presence of other components
3. dependent upon: nature of stationary phase (polarity), length of column, flow rate of gas
4. the more volatile component of a mixture will have the smaller retention time

Front 14

Partition Coefficients:

Back 14

1. dependent on solubility of component in liquid phase
2. solubility of a gas in liquid phase decreases a its vapor pressure increases, more volatile components pass through column more rapidly with liquid phase (polar w/carbowax, nonpolar with silicon gum rubber)

Front 15

How to detect components on GC:

Back 15

1. separate into bands
2. voltage proportional to mole fraction
3. flame ionization detector detects ions
4. but not all compound ionize to form same types or number of ions
5. so peak areas in chromatogram will not be exact unless corrected by RF

Front 16

Response Factors:

Back 16

-determine volume of each component that contributes using molar mass and density, scale down x100
-find ratio of peak areas
-

Front 17

Column Efficiency or Resolution:

Back 17

-increases with increasing column length, decrease diameter
-increase temp leads to shorter retention times because gas solubility in the liquid phase decreases at temp rises, up flow rate downs retention times

Front 18

Our substitution reaction was reversible, so it was performed in the excess of the _______________ and in the presence of _______ to add an H+

Back 18

Lewis Acid, H2SO4

Front 19

Verify that the SN2 occurred takes two tests:

Back 19

1. Addition of AgNO3 precips to get silver halide,,,halide colors: AgCl is white, AgBr is cream, AgI is bright yellow.
Fast reaction= tertiary, Slow reaction=primary... alkyl bromides and iodides are faster than chlorides

Front 20

Alkyl halide + NaI= insoluble NaCl or NaBr

speeds:

Back 20

primary bromides <3 at RT
primary chloride, NaCl if heated
2/3 bromides if heated
2/3 chlorides don't react

Front 21

Definition of Alkenes:

Back 21

organic compound where there is a polarizable C-C pi bond

Front 22

polarizable:

Back 22

ease with which e- cloud of a Lewis base is distorted by atom bearing a full or partial + charge

Front 23

bimolecular processes: elimination, substitution

Back 23

nuc attacks carbon bonded to leaving group form backside in e, or in s, it can pull acidic proton form beta carbon, moving its bonding electron to form a pi bond (ANTI PERI-PLANAR)

Front 24

unimolecular processes:

Back 24

nuc attacks carbocation in sub, in elim it pulls the acidic proton from c and forms a pi bond to alleviate positive charge on alpha carbon

Front 25

Substitution favored by which nuc's: Elim favored by which nuc's:

Back 25

1. weakly basic, highly polarizable nucleophiles (i-,br-,cl-h2o)
2. strongly basic, slightly polarizable nucs (ro-, oh-,nh2- h-) these bulky nuc's favor elim because its easier to remove a proton than approach a carbocation (also the more substituents the more likely elimination)

Front 26

Major product of an E2 is the _________ substituted on the double bond, its of lower energy

Back 26

most

Front 27

When can the major product be really the minor product in and E2?

Back 27

when the steric hinderance causes a nuc: to need to attack a less substituted carbon

Front 28

Alkanes are chemically non-reactive toward most reagents T or F

Back 28

True, except in free radical where an alkyl chloride or bromide forms x2--> 2Xdot, radical attacks R-H bond of alkane to give R-X + H

Front 29

GO OVER FREE RADICAL CHLORINATION OKAY?

Back 29

okay.

Front 30

In one of three termination steps, two alkane radicals can form a new sigma-bond, effectively forming a _______

Back 30

dimer

Front 31

Free radical halogenation of saturated alkanes produces both mono- and poly- substituted products: ex. 1-chlorobutane is chlorinated to get

Back 31

di-chloro and tri-chloro, poly-sub can be minimized by using excess alkane compared to reagent eg 2 alkane: 1 SO2Cl2

Front 32

If you perform the radical chlorination with care not avoid poly-sub then your end reaction "product mass" will really be...

Back 32

mass of actual dichlorobutanes + mass of unreacted 1-chlorobutane

Front 33

so before you do GC on a radical problem....

Back 33

you don't really actually know the masses

Front 34

zero % yield shows:

Back 34

mass of 1-chlorobutane used

Front 35

100 % yield shows:

Back 35

mass of number of moles of SO2Cl2 used (since its limiting and its 1:1:1) PLUS the difference between the mass of the #moles 1-cholorbutane used

Front 36

for 100% yield: mass in reaction flask at the end is the mass of:

Back 36

the number of moles of SO2Cl2 + (# moles started with - # moles used to create product) (all turned to grams)

Front 37

Theoretical yield:

Back 37

difference between the mass from zero product and 100 % product, it will be less than actual yield

Front 38

Experimental yield:

Back 38

difference between mass of mixture in the flask at the end (before drying) and the mass of o% yield

Front 39

once a GC is run, you can calculate the relative fraction of 1. the original reactant used which remains unreacted
vs 2. sum of all dichloro-products

to get...

Back 39

actual % yield

Front 40

The step that determines what products will form is the one which ------ which has a more likely to go?

Back 40

the 'H' is extracted from the alkane, H on an internal C because statistical factor

Front 41

Energetically, a secondary C-H is weaker than a primary C-H bond. True of False so what?

Back 41

True, so 1,2 dichloro and 1,3-dichloro are favored over 1,1 or 1,4. To determine statistical factor, take area under GC peak for each product and divide by #H capable of producing that product