lab final

Question 1

what is recrystalization used for and what is important for it?

Answer 1

useful technique for the purification of organic solids. the choice of solvent is important for it

Question 2

what does the solvent have to be like for recrystallization? how is the suitable solvent found?

Answer 2

solute has to be insoluble in the solvent at room temperature, but soluble in hot/boiling solvent. solubility test is done.

Question 3

how do the polar characteristics of a solvent and solute relate?

Answer 3

want slightly different polar characteristics

Question 4

during TLC, do polar or non polar components get eluted first? why is this? how does this show up on the tlc place?

Answer 4

non polar components get eluted first, because the more polar functional groups make stronger bonds with the absorbent (silica). this makes non polar compounds show up as higher on the tlc place.

Question 5

what happens if you increase the polarity of a solvent in tlc? using this, what would you do if the compounds were too close to the solvent front?

Answer 5

the solvent will dissolve more of the polar compounds (like dissolves like), causing the components to move up faster. if the compounds moved too close to the solvent front, it would be because the eluent was too polar and dissolved too much, so you would decrease the polarity of the solvent.

Question 6

what are two uses for tlc?

Answer 6

determining if a reaction has reached completion, or to determine if there are any impurities

Question 7

what are two ways in observing tlc plates?

Answer 7

under UV light, or stained with iodine vapor (dipped into staining solution and then held above heat until spots are visualized)

Question 8

what type of reaction is the diels-alder reaction?

Answer 8

[4+2]-cycloaddition between a conjugated diene and a dienophile

Question 9

what happens to the bonds in a diels-alder reaction?

Answer 9

2pi bonds are borken and 2 sigma bonds are formed in a concerted manner

Question 10

what happens if you use a cyclic diene in a diels-alder reaction?

Answer 10

synthesize bridged bicyclic compound

Question 11

in the diels alder lab, why did we flame dry the glassware?

Answer 11

because we were using maleic anhydride, which would undergo hydrolysis in the presence of water (which would change your final product)

Question 12

what type of reaction is a friedel-crafts reaction? what is used for these reactions and what is it called?

Answer 12

an electrophilic aromatic substitution reaction. aluminum chloride is used as a lewis acid catalyst (or iron (iii) chloride)

Question 13

why does the glassware have to be flame dried for the friedel crafts reactions?

Answer 13

iron (iii) chloride absorbs moisture

Question 14

what is a grignard reaction used for?

Answer 14

formation of c-c bonds

Question 15

when do grignard reactions decompose?

Answer 15

in the presence of protic solvents (water) or functional groups with acidic protons (alcohols, amines), to form alkanes. you need to make sure all glassware and reagents are dry

Question 16

why do you grind up the magnesium before starting the reaction?

Answer 16

to move oxide layer on the metal to activate the reaction

Question 17

what happens when you react grignard reagent (R-Mg-Br) with water?

Answer 17

form alkane R-H

Question 18

what happens with you react grignard reagent (R-Mg-Br) with o2?

Answer 18

form R-OH

Question 19

what is the main impurity in a grignard reaction? how is it formed?

Answer 19

the alkyl dimer (coupling product) R-R. formed from grignard reagent and alkyl halide

Question 20

what does reduction of a molecule refer to? what are two reducing agents?

Answer 20

addition of a hydrogen or removal of oxygen. LiBH4 (more powerful) and NaBH4

Question 21

what does LiBH4 reduce compared to NaBH4?

Answer 21

LiBH4 reduces carboxylic acids, esters, ketones and aldehydes. NaBH4 reduces ketones and aldehydes

Question 22

what do carboxylic acids, esters, and aldehydes get reduced to?

Answer 22

primary alcohols

Question 23

what do ketones get reduced to?

Answer 23

secondary alcohols

Question 24

how does the reducing agent work?

Answer 24

acts by transferring a hydride (H-) to the carbonyl group, forming an alkoxide that can be later protinated by water or an alcohol

Question 25

in the borohydride reduction, why did we add hcl at the end?

Answer 25

to protinate the alkoxide to turn it into the product

Question 26

what kind of reaction was used in the ether synthesis lab?

Answer 26

nucleophilic substitution reaction

Question 27

whats the point of sulfuric acid in the ether synthesis lab?

Answer 27

to protinate the hydroxyl group and make it a good leaving group

Question 28

what reducing agent is used in reductive amination? what does it reduce?

Answer 28

sodium triacetoxyborohydride Na(AcO)3BH, reduces imines to secondary amines.

Question 29

how can amines be prepared?

Answer 29

by reduction amination of imines (which are formed by a reaction between an amine and an aldehyde or ketone)

Question 30

what is a hemi aminal

Answer 30

an amino alcohol