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Chemistry Unit 3/4 > U4AOS1 - Analysis of Organic Compounds > Flashcards

U4AOS1 - Analysis of Organic Compounds Flashcards

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1
Q

What is the purpose of Mass-Spectroscopy

A

To measure the mass-to-charge (m/z) ratio of a molecule in a sample

Quantitative: shows the molecular mass of a sample

Qualitative: can provide insight into the branching of the molecule

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2
Q

How does Mass-Spectroscopy work?

A

Molecules are placed in a mass-spectroscopy machine, where they are ionized, producing positively charged fragments

The fragments produced may be the entire molecule, or a component of the molecule

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3
Q

Important thing to write with a fragment from Mass-Spec

A

Ensure that the molecule is positively charged (because its been ionized)

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4
Q

Molecular Ion Peak (on MS)

A

the largest peak on the graph - represents the full molecule (positively charged)

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5
Q

Base Peak (on MS)

A

the most abundant fragment (often created by a single split in the molecule) - assigned a relative abundance of 100%, with other fragments measured against it

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6
Q

Impact of Isotopes

A

Given isotopes have differing numbers of neutrons, they will appear at different m/z peaks on a mass-spec graph (could sometimes be higher than the ion peak)

They will generally have a small relative abundance relative to their low appearance in nature

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7
Q

X Axis of Mass Spectrum

A

Mass-to-Charge Ratio

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8
Q

Y Axis of Mass Spectrum

A

Relative Abundance

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9
Q

Purpose of Infrared Spectroscopy

A

Qualitative - to determine the bonds and the functional groups in an organic molecule

Quantitative - to determine the concentration of a solution

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10
Q

Principles of Infrared Spectroscopy

A

Different polar bonds absorb light at different wavelengths

Therefore - you can determine the bonds and functional groups by detecting which wavelengths of light are absorbed

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11
Q

X Axis of Infrared Spectra

A

Wavenumber (cm^-1)

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12
Q

Y Axis of Infrared Spectra

A

Transmittance (%)

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13
Q

Fingerprint Region

A

between 500-1400cm^-1

Unique for each molecule - don’t need to know how to read in VCE

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14
Q

Finding Hydroxyl Groups on Infrared Spectra

A

Roughly 3000-3400cm^-1

Carboxyl Acids - will be broad, and stretch below 3000cm^-1

Alcohols - will be above 3000cm^-1, and be skinner

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15
Q

Finding Carbonyl Groups on Infrared Spectra

A

Swords roughly between 1650 and 1850cm^-1

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16
Q

Finding N-H groups on Infrared Spectra

A

Swords at 3300-3500cm^-1

Primary Amine/Amides will have a single fang

Secondary Amine/Amides will have a single fang

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17
Q

Purpose of NMR

A

Quantitative: number of chemical environments environments

Quantative: ratio of atoms in an organic compound

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18
Q

Nucleus Spin States

A

A nucleus, with protons and neutrons, is able to behave like a magnet - in the absence of an external magnetic field, the nuclei will be randomly oriented

When a nucleus is placed in an external magnetic field (B0), it will either align with (low energy level) or against the field (high energy level)

The electrons around the nuclei oppose the external magnetic field, shielding the nucleus from its effect

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19
Q

Principles of NMR

A

A compound is placed within an external magnetic field, and the energy required to create a spin flip is recorded

20
Q

Use of TMS in NMR

A

TMS - tetramethylsilane, (CH3)4 Si)

An inert substance that will only produce a single peak

All other energy levels will be compared against TMR

21
Q

X Axis of NMR Spectra

A

Represents the chemical shifts (measured in ppm)

22
Q

Peaks in NMR Spectra

A

Represents a unique carbon/hydrogen environment

23
Q

H NMR Splitting Pattern

A

Because H NMR is high resolution, the peaks will split in accordance with the (n+1) rule

where n represents the number of hydrogens on the adjacent carbons

24
Q

H NMR Area under Peaks

A

the ratio of the area under the peaks can be used to determine the ratio of hydrogens in each particular hydrogen environment

25
Q

Purpose of Chromatography

A

Qualitative: determine the unknown components of a sample based upon its unique retention time

Qualitative: determine how much of a sample is produced (but requires a calibration curve)

26
Q

Principles of Chromatography

A

Each substance will have a unique retention time (time taken to flow through the column), based upon:

The attraction to its stationary phase (adsorption)
The attraction to its mobile phase (desoprtion)

27
Q

Does Chromatography destory the sample

A

No

28
Q

Mobile Phase

A

What the components of the sample dissolve into

29
Q

Stationary Phase

A

The surface that the mobile phase (and the sample) flows over

30
Q

What is HPLC

A

A chromatography technique - consists of a solid stationary phase, which is tightly packed into a glass column and a solvent that acts as the mobile phase

31
Q

What is Retention Time

A

The time taken for a component to pass through the column - depends on the extent to which the sample is attracted to the stationary vs the mobile phase

32
Q

Influence of a Longer Column on Retention Time

A

Will increase retention time

as it will take more time for the sample to flow through the column

33
Q

Influence of Increased Temperature on Retention Time

A

Will decrease retention time

as an increase in temperature increases the solubility of most substances (excluding gases) - which results in the substance being more strongly adsorbed into the mobile phase

34
Q

Influence of Increased Flow Rate of the Mobile Phase Retention Time

A

Decreases Retention Time

As the mobile phase is able to flow through the column faster, which will result in the sample flowing faster

35
Q

Influence of increasing surface area of the stationary phase on Retention Time

A

Increase Retention Time

Increased surface area results in stronger intermolecular bonds (greater surface for interactions), this results in the sample being more strongly adsorbed to the stationary phasei

36
Q

Purpose of Titration

A

Quantitative: to determine the unknown concentration of a solution

37
Q

Titration - Titrant

A

Solution of known concentration - placed into the burette

38
Q

Titration - Analyte

A

Sample solution of unknown concentration - placed into the conical flask

39
Q

How is a titrant conducted

A

The titrant is dispensed incrementally from the burette, and reacts gradually with the analyte.

This process continues until the change in color occurs (endpoint) - which can be seen with the presence of an indicator

40
Q

Titration - Equivalent Point

A

the point at which the titrant and the analyte have reacted to the stoichiometric ratio indicated in the balanced chemical equation

Occurs normally just after the endpoint (however - for the purposes of calculations we assume the endpoint is a good approximate of equivalence point)

41
Q

Titrations - Titre (and Concordant Titre)

A

Titre - the volume of titrant that is used to reach the endpoint

Concordant Titres - titres that are close together (usually within +-0.1mL(

42
Q

Neutralization Reaction

A

Acid + Base -> Ionic Salt + Water

43
Q

Acid - Base Titration (+ what to use for an indicator)

A

Determines the concentration of acids or bases via a neutralisation reaction between the two substances

For an indicator: use an indicator that falls within the pH of the equivalence point

44
Q

Equivalence Point for Acid/Base Titrations

A
45
Q

Redox Titrations (+ what to use for an indicator)

A

Redox Reaction between the oxidizing and reducing agent

For an indicator: often the reaction itself involves substances that change color as a result of the redox reaction - which means they may not require the use of an indicator

Exceptions: for reactions involving iodine - use starch as an indicator

Chemistry Unit 3/4 (16 decks)

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