BS21012 Core Lab Skills 2A

Question 1

A carboxylic acid and an alcohol form to make…

Answer 1

An ester and water

Question 2

the reaction to make an ester is called…

Answer 2

Acid catalysed ester formation

Question 3

The reverse reaction of ester formation is called…

Answer 3

Acid catalysed ester hydrolysis or enzyme-catalysed ester hydrolysis

Question 4

orange peel and pig liver esterases are a class of esterases belonging to a family called…

Answer 4

Carboxylesterases.

Question 5

Pig liver esterase is a…

Answer 5

serine hydrolase

Question 6

What are the two key steps in serine hydrolase’s mechanism of ester hydrolysis…

Answer 6

Nucloephilic addition of serine to the carbonyl group of the ester.
Collapse of the tetrahedral intermediate

Question 7

What is the “regeneration of the catalytic triad”…

Answer 7

The covalent adduct with the substrate is hydrolysed in a reaction with water that is catalysed by the proximity of the nucleophilic imidazole ring of histidine

Question 8

Orange peel esterase is a pectin-esterase which is a(n)…

Answer 8

an enzyme that catalyses the hydrolysis of pectin into pectate and methanol

Question 9

Pectin is a polysaccharide characterized by…

Answer 9

Repeated units of Methylated galacturonic acid (Gal A)

Question 10

A molecule made of repeated units of Methylated galacturonic acid (Gal A) is called…

Answer 10

Pectin (polysaccharide)

Question 11

give examples of processes in which de-esterification of pectin is important…

Answer 11

Cell wall metabolism
Fruit ripening
Pollen germination
Plant resistance to pathogen attack

Question 12

Where can acetylcholine esterases be found… (2 places)

Answer 12

in the postsynaptic cell membrane of the neuromuscular junction
Cholinergic neurons in the brain

Question 13

What do Acetylcholine esterases do…

Answer 13

It hydrolyses acetylcholine, a neurotransmitter, into choline and acetate

Question 14

What have the reverse inhibitors of acetylcholine been shown to interact with… (diseases)

Answer 14

Alzheimer’s disease, Myasthenia grans, glaucoma.

Question 15

Irreversible inhibitors of acetylcholine are known to be involved in…

Answer 15

toxins, insecticides, and nerve agents

Question 16

What are the symptoms of acute poisoning from acetylcholine inhibitors…

Answer 16

Agitation, muscle weakness, sweating, respiratory failure, confusion/ unconsciousness, convulsions and/or death

Question 17

Infra red radiation…

Answer 17

excites the stretching vibration of bonds and deformation vibrations of bond angles

Question 18

What must a bond have for IR to have an effect…

Answer 18

The bond must have a dipole-dipole attraction

Question 19

IR has a ____ wavelength than than visible light and ____ energy

Answer 19

Greater wavelength and less energy

Question 20

An IR spectrum shows…

Answer 20

Characteristics for a single molecule

Question 21

What do the peaks in an IR spectrum represent

Answer 21

The peaks represent specific functional groups

Question 22

What do the X and Y axis show on an IR spectrum graph

Answer 22

The X-axis shows wavenumber (cm-1), and the Y-axis shows IR absorbance

Question 23

What are the 2 main descriptions of IR peaks…

Answer 23

Sharp or broad (sp or b)

Question 24

What are the 4 classifications of intensity in IR peaks…

Answer 24

Very strong (VS) >90% absorption
Strong (S) 70-90% absorption
Medium (M) 50-70% absorption
Weak (W) <40% absorption

Question 25

Where X is an element what is the IR stretch of X-H

Answer 25

3500-3100cm-1

Question 26

Give examples of X-H stretches, a description of their peak, the intensity of the peak, and the name of the group...

Answer 26

O-H, S, B, alcohols and phenols O-H, S, VB, Acids N-H, S, Sp, 1' amines/amides or 2' amines/amides

Question 27

C-H stretch is in what range on an IR spectrum

Answer 27

3300-2700cm-1

Question 28

Name the three different groups of C-H groups in IR

Answer 28

Aromatic - 3150-3000cm-1, W-M Alkenic - 3050-2950cm-1, W-M Alkanic - 2950-2850cm-1, W-M

Question 29

Name the two other types of C-H stretch (irregularities)

Answer 29

Terminal Alkynes (if the weak peak of C-C) (a triple bond is found near 2200cm-1), 3300cm-1, S Aldehyde - 2850-2700cm-1, W-M, O=C-H bond (two peaks)

Question 30

What is the range of the C=O stretch

Answer 30

1850-1550cm-1

Question 31

What are four examples of C=O stretches on an IR spectrum

Answer 31

Anhydride - 1850-1800cm-1, VS, (second peak at 1750) Carboxylic acid Halide - 1820-1750cm-1, VS Ester - 1750-1710, VS aldehyde - 1740-1690, VS (only if C-H peaks present)

Question 32

Name the other four examples of C=O stretches

Answer 32

Ketone - 1730-1650cm-1, VS Carboxylic acid - 1720-1680cm-1, VS Carboxylic acid anion, 1650-1550cm-1, VS Amide - 1670-1630cm-1, VS, (2 bonds, the second is at 1560-1510cm-1)

Question 33

What is an key observation about the overlapping in the IR spectrum

Answer 33

There can be overlaps between the intensity readings, the structure is then determined using knowledge of the shape and structure of molecules.

Question 34

For a compound to be classed as aromatic it must have the following features

Answer 34

A C-H stretch at 3150-3000cm-1, W-M (usually weak) A C-C stretch at 1600-1500cm-1, W-S, (sharp but 1600 is not always present) A C-H deformation at 900-600, M-S (usually strong)

Question 35

if a compound is not aromatic in IR it must be...

Answer 35

Aliphatic (linear)

Question 36

What are the key characteristics of an Aliphatic molecule

Answer 36

If the C-H stretch absorptions are al below 3000cm-1 and there are no strong series at 900-600cm-1, the compound is aliphatic and contains no C-C bonds

Question 37

If an -OH group is found at 3500-3100cm-1 what are the two types of compound it could be apart of

Answer 37

Alcohol or phenol

Question 38

if there is an OH group at 3500-3100cm-1 what is the range the C-O stretch will be found in for it to be an alcohol or a phenol

Answer 38

1250-1050cm-1

Question 39

what is the intensity value for a phenols C-O stretch

Answer 39

1200cm-1, VS

Question 40

what are the three different intensities of alcohols C-O group and what do they correspond to

Answer 40

Primary, secondary and tertiary alcohols all have different intensities Primary, near 1050cm-1, VS secondary, near 1100cm-1, VS tertiary, near 1150cm-1, VS

Question 41

What is the difference in IR between amines and amides

Answer 41

if a sharp peak(s) is found at 3500-3300cm-1 then the conformation of an amide will be seen through a C=O stretch at 1670-1620cm-1. if this is not present then it is an amine

Question 42

What are the distinctions between 1' and 2' amines

Answer 42

1' amines normally show two N-H peaks | 2' amines only show one N-H peak

Question 43

what are the intensity ranges for amines

Answer 43

N-H deformation, 1650-1500cm-1, M, (1' amines) N-H deformation 1580-1500cm-1, M-W, (2' amines) C-N stretch, 1350-1270cm-1, M-S (not always seen)

Question 44

How are carbonyl compounds identified

Answer 44

They are identified through the expected additional features either in the primary or confirmatory region