What is the difference in purpose between heating under reflux and distillation in organic chemistry?

Heating under reflux keeps all chemicals inside the reaction vessel to allow a reaction to proceed as fully as possible. Distillation is used to separate a desired product from a mixture by exploiting differences in boiling point .

Define molecular ion in mass spectroscopy

The molecular ion (M + ) is formed when a molecule is bombarded with high-energy electrons and loses one electron, producing a positively charged ion with one unpaired electron. The peak with the highest m/z value in a mass spectrum corresponds to the molecular ion and gives the molecular mass of the compound.

Define infrared (IR) spectroscopy

Infrared spectroscopy is an analytical technique used to identify compounds based on the absorption of infrared radiation by bonds in a molecule. When bonds absorb IR radiation at their resonance frequency, they vibrate by stretching, bending or twisting, and the absorbed frequencies are characteristic of specific functional groups.

Why is an electric heating mantle used instead of a Bunsen burner when distilling organic compounds?

Electric heating mantles allow the temperature to be controlled more precisely. They are also safer because organic compounds are often flammable , and an open Bunsen burner flame poses a fire or explosion risk.

Define base peak in a mass spectrum

The base peak is the peak corresponding to the most abundant ion fragment in a mass spectrum. It is the tallest peak in the spectrum and is given a relative abundance of 100%.

Define wavenumber in infrared spectroscopy

Wavenumber (units: cm -1 ) is the reciprocal of the wavelength of infrared radiation. It is used on the x-axis of an IR spectrum to show at which frequencies specific bonds absorb IR radiation.

A pure compound has a sharp , .......... boiling point. If impurities are present, the boiling point may appear .......... than the literature value or the sample may boil over a .......... of temperatures.

A pure compound has a sharp , single boiling point. If impurities are present, the boiling point may appear higher than the literature value or the sample may boil over a range of temperatures.

What causes the [M+1] peak in a mass spectrum?

The [M+1] peak is caused by the natural abundance of the carbon-13 isotope (just over 1%). Molecules containing C-13 instead of C-12 have a mass one unit higher than the molecular ion. The larger the number of carbon atoms in the molecule, the taller the [M+1] peak.

What do the width and intensity of an IR absorption peak tell us about a bond?

The width indicates whether the absorption is broad or sharp : for example, O-H bonds in alcohols absorb broadly due to hydrogen bonding. The intensity indicates whether it is strong or weak : the C=O carbonyl group gives a strong, sharp absorption peak.

True or False? In a condenser, cooling water enters at the top and exits at the bottom.

False. Cooling water enters at the bottom of the condenser and exits at the top. This counter-current flow maximises cooling efficiency.

How is the m/z ratio calculated and which ions are deflected most in a mass spectrometer?

The m/z ratio is calculated as the mass (m) of the ion divided by its charge (z). Ions with a small m/z ratio (small mass or high positive charge) are deflected the most and are detected first.

Describe the characteristic IR absorption of the O-H group in an alcohol.

The O-H group in an alcohol gives a broad , strong absorption in the region of approximately 3200-3500 cm -1 . The broadness is due to the varying strengths of hydrogen bonds between alcohol molecules.

Describe how a separating funnel is used to isolate an organic product from an aqueous layer.

The mixture is transferred to a separating funnel and inverted with the stopcock open to release pressure, repeating this several times. The two layers are allowed to separate, then the lower aqueous layer is drained off through the stopcock and the organic layer is collected separately.

In a mass spectrum, the peak with the .......... m/z value corresponds to the .......... ion and gives the .......... of the compound.

In a mass spectrum, the peak with the highest m/z value corresponds to the molecular ion and gives the molecular mass of the compound.

Describe the characteristic IR absorption of the C=O (carbonyl) group in a ketone.

The C=O group in a ketone gives a strong , sharp absorption at approximately 1710 cm -1 . This peak is distinct and easily identified in an IR spectrum.

What is the purpose of using a drying agent in the purification of an organic product?

A drying agent is an anhydrous inorganic salt used to remove trace amounts of water from an organic product. Common drying agents include anhydrous calcium chloride (for hydrocarbons) and anhydrous calcium or magnesium sulfate (for general use).

True or False? The base peak in a mass spectrum is always the molecular ion peak.

False. The base peak is the most abundant ion, which is often a fragment rather than the molecular ion. The molecular ion peak has the highest m/z value but is not always the most abundant.

In IR spectroscopy, molecules absorb IR radiation at their .......... frequency, causing bonds to .......... by stretching, bending or twisting.

In IR spectroscopy, molecules absorb IR radiation at their resonance frequency, causing bonds to vibrate by stretching, bending or twisting.

True or False? If the drying agent clumps together, the organic product is dry and no more drying agent is needed.

False. Clumping means the drying agent has absorbed water and water is still present in the organic liquid. More drying agent must be added until some remains dispersed as a fine powder.

Why do halogenoalkanes show two peaks of similar height near the molecular ion in a mass spectrum?

Halogens exist as isotopes with different masses (e.g. 79 Br and 81 Br in roughly equal natural abundance). Each isotope produces a molecular ion with a different m/z value, resulting in two peaks of approximately equal height at M and M+2.

True or False? All organic molecules absorb infrared radiation.

True. All organic molecules absorb IR radiation. The specific frequencies absorbed depend on the bonds and functional groups present, which is what makes IR spectroscopy useful for identifying compounds.

An aldehyde distils off more easily than the primary alcohol used to make it because the aldehyde has a .......... boiling point, as it has lost the ability to form .......... bonds.

An aldehyde distils off more easily than the primary alcohol used to make it because the aldehyde has a lower boiling point, as it has lost the ability to form hydrogen bonds.

What characteristic fragment peak do alcohols typically show in mass spectra?

Alcohols commonly show a peak at m/z = 31, corresponding to the CH 2 OH + fragment. They also often show a peak 18 units below the molecular ion peak, due to the loss of a water molecule.

Why should IR spectroscopy be used alongside mass spectroscopy to identify an unknown compound?

Some IR absorption bands overlap each other, making it impossible to distinguish between certain functional groups from IR alone. Mass spectroscopy provides molecular mass and fragmentation data that complement IR data to give a more complete structural identification.

True or False? Anti-bumping granules are added to prevent the reaction mixture from boiling.

False. Anti-bumping granules are added to promote smooth boiling . They provide nucleation sites for bubbles, preventing sudden violent boiling (bumping).

In the mass spectrum of propan-1-ol, the loss of a • C 2 H 5 radical gives a fragment with m/e = .......... corresponding to the ion .......... + .

In the mass spectrum of propan-1-ol, the loss of a • C 2 H 5 radical gives a fragment with m/e = 31 corresponding to the ion CH 2 OH + .

How is an unknown compound identified using infrared spectroscopy?

The IR spectrum of the unknown compound is compared with the IR spectra of known compounds in a database. Absorption peaks at characteristic wavenumbers identify the functional groups present, allowing the compound to be identified.

How can you identify which layer is organic and which is aqueous in a separating funnel?

Add a small amount of water to the separating funnel and observe which layer increases in volume. The layer that increases is the aqueous layer.

Why is fragmentation useful when identifying an unknown compound by mass spectrometry?

Different compounds may have the same molecular mass, so the molecular ion peak alone cannot distinguish between them. Fragmentation produces characteristic peaks at specific m/z values that reveal structural information about the molecule.

International A Level (IAL)ChemistryEdexcelFlashcards2. Energetics, Group Chemistry, Halogenoalkanes & AlcoholsOrganic Chemistry: Techniques & Spectra

Organic Chemistry: Techniques & Spectra (Edexcel International A Level (IAL) Chemistry): Flashcards

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What is the difference in purpose between heating under reflux and distillation in organic chemistry?

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What is the difference in purpose between heating under reflux and distillation in organic chemistry?
Heating under reflux keeps all chemicals inside the reaction vessel to allow a reaction to proceed as fully as possible.
Distillation is used to separate a desired product from a mixture by exploiting differences in boiling point.
Define molecular ion in mass spectroscopy
The molecular ion (M⁺) is formed when a molecule is bombarded with high-energy electrons and loses one electron, producing a positively charged ion with one unpaired electron.
The peak with the highest m/z value in a mass spectrum corresponds to the molecular ion and gives the molecular mass of the compound.
Define infrared (IR) spectroscopy
Infrared spectroscopy is an analytical technique used to identify compounds based on the absorption of infrared radiation by bonds in a molecule.
When bonds absorb IR radiation at their resonance frequency, they vibrate by stretching, bending or twisting, and the absorbed frequencies are characteristic of specific functional groups.
Why is an electric heating mantle used instead of a Bunsen burner when distilling organic compounds?
Electric heating mantles allow the temperature to be controlled more precisely.
They are also safer because organic compounds are often flammable, and an open Bunsen burner flame poses a fire or explosion risk.
Define base peak in a mass spectrum
The base peak is the peak corresponding to the most abundant ion fragment in a mass spectrum.
It is the tallest peak in the spectrum and is given a relative abundance of 100%.
Define wavenumber in infrared spectroscopy
Wavenumber (units: cm^-1) is the reciprocal of the wavelength of infrared radiation.
It is used on the x-axis of an IR spectrum to show at which frequencies specific bonds absorb IR radiation.
A pure compound has a sharp, .......... boiling point. If impurities are present, the boiling point may appear .......... than the literature value or the sample may boil over a .......... of temperatures.
A pure compound has a sharp, single boiling point. If impurities are present, the boiling point may appear higher than the literature value or the sample may boil over a range of temperatures.
What causes the [M+1] peak in a mass spectrum?
The [M+1] peak is caused by the natural abundance of the carbon-13 isotope (just over 1%).
Molecules containing C-13 instead of C-12 have a mass one unit higher than the molecular ion. The larger the number of carbon atoms in the molecule, the taller the [M+1] peak.
What do the width and intensity of an IR absorption peak tell us about a bond?
The width indicates whether the absorption is broad or sharp: for example, O-H bonds in alcohols absorb broadly due to hydrogen bonding.
The intensity indicates whether it is strong or weak: the C=O carbonyl group gives a strong, sharp absorption peak.
True or False?
In a condenser, cooling water enters at the top and exits at the bottom.
False.
Cooling water enters at the bottom of the condenser and exits at the top. This counter-current flow maximises cooling efficiency.
How is the m/z ratio calculated and which ions are deflected most in a mass spectrometer?
The m/z ratio is calculated as the mass (m) of the ion divided by its charge (z).
Ions with a small m/z ratio (small mass or high positive charge) are deflected the most and are detected first.
Describe the characteristic IR absorption of the O-H group in an alcohol.
The O-H group in an alcohol gives a broad, strong absorption in the region of approximately 3200-3500 cm^-1.
The broadness is due to the varying strengths of hydrogen bonds between alcohol molecules.
Describe how a separating funnel is used to isolate an organic product from an aqueous layer.
The mixture is transferred to a separating funnel and inverted with the stopcock open to release pressure, repeating this several times.
The two layers are allowed to separate, then the lower aqueous layer is drained off through the stopcock and the organic layer is collected separately.
In a mass spectrum, the peak with the .......... m/z value corresponds to the .......... ion and gives the .......... of the compound.
In a mass spectrum, the peak with the highest m/z value corresponds to the molecular ion and gives the molecular mass of the compound.
Describe the characteristic IR absorption of the C=O (carbonyl) group in a ketone.
The C=O group in a ketone gives a strong, sharp absorption at approximately 1710 cm^-1.
This peak is distinct and easily identified in an IR spectrum.
What is the purpose of using a drying agent in the purification of an organic product?
A drying agent is an anhydrous inorganic salt used to remove trace amounts of water from an organic product.
Common drying agents include anhydrous calcium chloride (for hydrocarbons) and anhydrous calcium or magnesium sulfate (for general use).
True or False?
The base peak in a mass spectrum is always the molecular ion peak.
False.
The base peak is the most abundant ion, which is often a fragment rather than the molecular ion. The molecular ion peak has the highest m/z value but is not always the most abundant.
In IR spectroscopy, molecules absorb IR radiation at their .......... frequency, causing bonds to .......... by stretching, bending or twisting.
In IR spectroscopy, molecules absorb IR radiation at their resonance frequency, causing bonds to vibrate by stretching, bending or twisting.
True or False?
If the drying agent clumps together, the organic product is dry and no more drying agent is needed.
False.
Clumping means the drying agent has absorbed water and water is still present in the organic liquid. More drying agent must be added until some remains dispersed as a fine powder.
Why do halogenoalkanes show two peaks of similar height near the molecular ion in a mass spectrum?
Halogens exist as isotopes with different masses (e.g. ⁷⁹Br and ⁸¹Br in roughly equal natural abundance).
Each isotope produces a molecular ion with a different m/z value, resulting in two peaks of approximately equal height at M and M+2.
True or False?
All organic molecules absorb infrared radiation.
True.
All organic molecules absorb IR radiation. The specific frequencies absorbed depend on the bonds and functional groups present, which is what makes IR spectroscopy useful for identifying compounds.
An aldehyde distils off more easily than the primary alcohol used to make it because the aldehyde has a .......... boiling point, as it has lost the ability to form .......... bonds.
An aldehyde distils off more easily than the primary alcohol used to make it because the aldehyde has a lower boiling point, as it has lost the ability to form hydrogen bonds.
What characteristic fragment peak do alcohols typically show in mass spectra?
Alcohols commonly show a peak at m/z = 31, corresponding to the CH₂OH⁺ fragment.
They also often show a peak 18 units below the molecular ion peak, due to the loss of a water molecule.
Why should IR spectroscopy be used alongside mass spectroscopy to identify an unknown compound?
Some IR absorption bands overlap each other, making it impossible to distinguish between certain functional groups from IR alone.
Mass spectroscopy provides molecular mass and fragmentation data that complement IR data to give a more complete structural identification.
True or False?
Anti-bumping granules are added to prevent the reaction mixture from boiling.
False.
Anti-bumping granules are added to promote smooth boiling. They provide nucleation sites for bubbles, preventing sudden violent boiling (bumping).
In the mass spectrum of propan-1-ol, the loss of a ^•C₂H₅ radical gives a fragment with m/e = .......... corresponding to the ion ..........⁺.
In the mass spectrum of propan-1-ol, the loss of a ^•C₂H₅ radical gives a fragment with m/e = 31 corresponding to the ion CH₂OH⁺.
How is an unknown compound identified using infrared spectroscopy?
The IR spectrum of the unknown compound is compared with the IR spectra of known compounds in a database.
Absorption peaks at characteristic wavenumbers identify the functional groups present, allowing the compound to be identified.
How can you identify which layer is organic and which is aqueous in a separating funnel?
Add a small amount of water to the separating funnel and observe which layer increases in volume.
The layer that increases is the aqueous layer.
Why is fragmentation useful when identifying an unknown compound by mass spectrometry?
Different compounds may have the same molecular mass, so the molecular ion peak alone cannot distinguish between them.
Fragmentation produces characteristic peaks at specific m/z values that reveal structural information about the molecule.

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