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OChem 1 lab > Midterm CHM 254 > Flashcards

Midterm CHM 254 Flashcards

1
Q

Lab 2

Index of Hydrogen Deficency

A

(C+1)+(N-H-X)/2

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2
Q

Lab 2

Explain a brief procedure of recrystallization

A
  1. add product to water and boil until dissolve
  2. hot filtration
  3. cold filtration with vacuum
  4. take mp of dried crystals
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3
Q

Lab 2

eutectic point

A

the lowest possible melting point of a mixture

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4
Q

Lab 2

melting point

A

where the liquid and vapor phases co exist

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5
Q

lab 2

Percent recovery

A

m recovered/ mass initial

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6
Q

Lab 2

percent recovery

w/o mass values

A

(1-Sc/Sh)*100

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7
Q

Lab 2

Name some essential parts of choosing a solvent for recrystallization

A
  1. the wanted product should be very soluble in hot solvent and very insoluble in cold solvent
  2. bp of solvent should be lower than the mp of the wanted product
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8
Q

Lab 3

Brief Procedure of extraction

Extraction of caffeine from tea

A
  1. obtain tea+ CaCO3 + water and boil
  2. cool boiled liquid and vacuum filter
  3. set up sep. funnel and add filtered liquid + organic solvent + salt and shake to mix
  4. Dry collected organic layer over MgSO4
  5. gravity filter dried layer
  6. rotovap
  7. perform recrystallization w/ hot acetone + pet ether
  8. take m.p of recrystallized caffeine
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9
Q

lab 3

organic layer

A

the phase you want, compound + organic solvent

usually less dense than water

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10
Q

lab 3

aq. phase

A

the water layer, water + any other impurities

usually more dense than organic solvent

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11
Q

lab 3

Partition coefficient definition

A

equilibrium constant that determines the distribution of a solute between two solvents

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12
Q

lab 3

Partition coefficent using solubilites

A

solubility of solute in organic solvent/solubility of solute in aq solvent

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13
Q

lab 3

partition coefficient using concentration

A

the concentration of solute in organic layer/ concentration of solute in aq layer

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14
Q

lab 3

partition coefficent >1

A

favors organic layer

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15
Q

lab 3

partition coefficient < 1

A

favors aq layer

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16
Q

lab 3

How do you determine the organic layer?

A

Density! Organic solvents are usually less dense than water and will be on top. Determine which solvent is less dense to know which layer is which.

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17
Q

lab 3

why do you rotovap something?

A

to get rid of any additional organic solvent and obtain a solid product

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18
Q

lab 3

How would you choose an organic solvent for extraction?

A
  1. like dissolves like, chose a solvent that matches the polarity of the wanted compound
  2. pick one with a large partition coefficent
  3. Immiscible w/ water
19
Q
A
20
Q

lab 4

Ir spectroscopy

A

the spectroscopy of functional groups

21
Q

lab 4

Dipole moment

A

separated positive and negative charges on a molecule due to differences in electronegativity

22
Q

lab 4

how does having a dipole moment affect IR spectra?

A

The greater the change in dipole moment during vibrational patterns the greater the absorption peak on the graph. So molecules with greater dipole moments will have greater absorptions

23
Q

lab 4

what does it mean to be IR active?

A

To be IR active there must be a change in your dipole moment during your stretching patterns. Diatomics and C-C or C=C bonds don’t have strong or any dipole moments to change.

24
Q

lab 4

In IR spectra a molecule can only move from the — energy state to the — — energy state

A

lowest, second lowest

n=0 to n=1

25
Q

lab 4

Why does asymmetric stretching produce a more intense peak than symmetric stretching?

A

Asymmetric stretching creates a greater change in dipole moment than symmetric stretching.

26
Q

lab 5

Procedure for TLC plates

A
  1. obtain and cut spinach, add add methanol and crush
  2. drain liquid, add hexanes and methanol, and crush again
  3. drain into sep funnel, add water and shake
  4. dry over sodium sulfate and gravity filter with cotton
  5. rotovap
  6. preapre TLC plates w/ determined number of applications
27
Q

lab 5

what are the four solvents we prepared for TLC plates

A

hexanes: ethyl acetane (9:1)
hexanes: ethyl acetane (7:3)
hexanes
ethyl acetane

28
Q

lab 5

are hexanes polar or non polar

A

non polar

29
Q

lab 5

stationary phase

A

the phase applied to the plates, has the binding sites

29
Q

lab 5

is ethyl acetane polar or non polar

A

polar

30
Q

lab 5

mobile phase

A

the solvent used, travels up the plate

31
Q

lab 5

origin line

A

where the applications of solute are placed and where the solvent begins

32
Q

lab 5

solvent front

A

where the solvent stops

33
Q

lab 5

ratio to the front (rF)

A

the difference in the distance from the spot traveled to the solvent front

34
Q

lab 5

Rf=

A

distance traveled by spot/ distance traveled by solvent = spot/solvent

35
Q

lab 5

what is a binding site and why does it matter?

A

A binding site is where the mobile phase and the solute particles compete to bind to spots on the stationary phase

36
Q

lab 5

what are the most commonly used stationary phases for TLC plates?

A

silica and alumina

37
Q

lab 5

How would you chose a solvent for a TLC plate?

A
  1. a polar solvent for polar mixture
  2. a np solvent for a np mixture
  3. if you have a mixure of polar and np then a mixture of the two will be needed for solvent
38
Q

lab 5

would a polar or non polar solute travel further in a polar and non polar solvent mixture

A

non polar would likely travel further because it likely does not have electrophilic atoms that would form hydorgen bonds at the binding sites.

39
Q

C-NMR

Each peak corresponds to — on a C-NMR

A

set of equivalent carbons

40
Q

C-NMR

Which side of a NMR is considered up field and downfield?

A

Left side is upfield, higher energy, deshielded
Right side is downfield, lower energy and shielded

41
Q

C-NMR

Do pi bonds have higher or lower chemical shift on an NMR?

A

Higher chemical shift

important for carbonyl bonds and aromatics

42
Q

C-NMR

Do alkanes have higher and or lower shifts?

A

lower shifts

sp3 atoms have low shifts

OChem 1 lab (2 decks)

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