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24:[["$","$L33",null,{"feature":"flashcards"}],"$L34",["$","$L35",null,{"href":"/a-level/chemistry/edexcel/infrared-spectroscopy/flashcards","label":"Infrared spectroscopy","subjectCode":"a_level_chemistry","surface":"flashcards"}],["$","$L36",null,{"runner":["$","div",null,{"className":"min-h-0 flex-1 overflow-hidden bg-background","children":["$","$L37",null,{"decks":[{"id":"2d9d813f-e703-43cb-8320-0e910b4088d1","title":"Infrared spectroscopy Flashcards","topicId":"7b9d5529-da12-5a5c-9988-d7e10ad82d9b","topicSlug":"infrared-spectroscopy","cards":[{"id":"f509b6f6-d7cf-4bc8-b0be-d04b3db63949","cardType":"cloze","points":null,"front":"Covalent bonds can vibrate by [ ] or [ ].","back":"Covalent bonds can vibrate by stretching or bending.","mcqOptions":[{"text":"Covalent bonds can vibrate by stretching or bending.","correct":true,"explanation":"Stretching changes the distance between bonded atoms, whereas bending changes the angle between bonds. These are the two principal categories used to describe molecular vibrations."},{"text":"Covalent bonds can vibrate by translating or bending.","correct":false,"explanation":"Translation describes movement of the whole molecule through space, not vibration within a bond. Covalent-bond vibrations are classified as stretching or bending."},{"text":"Covalent bonds can vibrate by stretching or rotating.","correct":false,"explanation":"Rotation changes the orientation of the whole molecule rather than its bond lengths or angles. Covalent bonds vibrate through stretching and bending motions."},{"text":"Covalent bonds can vibrate by translating or rotating.","correct":false,"explanation":"Translation and rotation are forms of whole-molecule motion, not the two principal bond-vibration categories. Those categories are stretching and bending."}]},{"id":"ab435d0f-b892-4b6b-8c6d-01fcb35f384e","cardType":"basic","points":1,"front":"What must match for a covalent bond to absorb infrared radiation?","back":"The IR frequency must match an allowed vibrational frequency.","mcqOptions":[{"text":"The IR frequency must match an allowed vibrational frequency.","correct":true,"explanation":"Absorption occurs when the frequency of incoming infrared radiation equals an allowed vibrational frequency, enabling the molecule to move between quantised vibrational energy levels."},{"text":"The IR amplitude must match an allowed vibrational frequency.","correct":false,"explanation":"Matching amplitudes does not determine photon absorption because photon energy depends on frequency. The IR frequency must equal an allowed vibrational frequency of the bond."},{"text":"The IR intensity must match an allowed vibrational frequency.","correct":false,"explanation":"Intensity affects how many suitable photons arrive, not whether their energy fits a vibrational transition. The IR frequency must match an allowed vibrational frequency."},{"text":"The IR phase must match an allowed vibrational frequency.","correct":false,"explanation":"A phase match is not the resonance condition for infrared absorption. Absorption requires the radiation frequency to coincide with an allowed molecular vibrational frequency."}]},{"id":"e56727ab-4ea8-4e54-bd97-2bd93799c181","cardType":"cloze","points":null,"front":"An IR-active vibration must change the molecule’s [ ].","back":"An IR-active vibration must change the molecule’s dipole moment.","mcqOptions":[{"text":"dipole moment","correct":true,"explanation":"An oscillating infrared electric field can interact with a vibration only when that vibration produces a changing dipole moment, making the mode IR-active."},{"text":"polarizability","correct":false,"explanation":"A change in polarizability is the selection rule associated with Raman activity, not IR activity. An IR-active vibration must produce a change in dipole moment."},{"text":"bond enthalpy","correct":false,"explanation":"Bond enthalpy influences bond strength and therefore vibrational frequency, but changing it is not the IR selection rule. The vibration must change the molecular dipole moment."},{"text":"molecular mass","correct":false,"explanation":"Molecular mass affects vibrational frequencies but remains constant during a vibration. IR activity requires the molecule’s dipole moment to change as it vibrates."}]},{"id":"7f0e3f97-d22c-4b34-836c-613a53d7ecde","cardType":"basic","points":2,"front":"Why can IR spectroscopy suggest which functional groups are present?","back":"Different bonds absorb at characteristic wavenumber ranges.","mcqOptions":[{"text":"Different bonds absorb at characteristic wavenumber ranges.","correct":true,"explanation":"Bond strength and the masses of the bonded atoms determine vibrational frequency, so different bond types absorb within characteristic wavenumber ranges that indicate functional groups."},{"text":"Different colours absorb at characteristic wavenumber ranges.","correct":false,"explanation":"Molecular colours arise from interactions with visible light and do not identify IR vibrational absorptions. Different bond types absorb infrared radiation at characteristic wavenumber ranges."},{"text":"Different isotopes absorb at characteristic wavenumber ranges.","correct":false,"explanation":"Isotopes can shift absorption positions slightly, but they are not the main basis for functional-group identification. Different bonds have characteristic IR wavenumber ranges."},{"text":"Different spins absorb at characteristic wavenumber ranges.","correct":false,"explanation":"Electron spins are investigated by techniques such as EPR rather than by ordinary IR vibrational spectroscopy. Different bonds absorb in characteristic wavenumber ranges."}]},{"id":"d385b641-4759-4518-8a84-2833ca3f036e","cardType":"basic","points":2,"front":"Which equations link radiation energy, frequency and wavelength?","back":"

$E = hν$
$ν = c/λ$

","mcqOptions":[{"text":"

$E = hν$
$ν = c/λ$

","correct":true,"explanation":"Planck’s relation gives photon energy as frequency multiplied by Planck’s constant, while wave speed equals frequency multiplied by wavelength, giving frequency as $c/λ$."},{"text":"

$E = h/ν$
$ν = cλ$

","correct":false,"explanation":"Dividing Planck’s constant by frequency reverses the energy-frequency relationship, while multiplying $c$ by wavelength is dimensionally incorrect. The equations are $E=hν$ and $ν=c/λ$."},{"text":"

$E = hcλ$
$ν = λ/c$

","correct":false,"explanation":"Multiplying $hc$ by wavelength gives the wrong wavelength dependence, and $λ/c$ has units of time. The correct relations are $E=hν$ and $ν=c/λ$."},{"text":"

$E = ν/h$
$ν = λ/c$

","correct":false,"explanation":"Frequency must multiply, not divide by, Planck’s constant to give energy. Frequency is also wave speed divided by wavelength, so the equations are $E=hν$ and $ν=c/λ$."}]},{"id":"c80ed38b-6915-48e4-a829-370d4e392768","cardType":"basic","points":2,"front":"How do you calculate wavenumber from wavelength in IR spectroscopy?","back":"

Wavenumber = 1/λ
Use λ in cm for cm^-1

","mcqOptions":[{"text":"

Wavenumber = 1/λ
Use λ in cm for cm^-1

","correct":true,"explanation":"Wavenumber is the reciprocal of wavelength. Because IR spectra conventionally use cm^-1, wavelength must first be expressed in centimetres before taking its reciprocal."},{"text":"

Wavenumber = λ
Use λ in cm for cm^-1

","correct":false,"explanation":"Wavenumber counts waves per unit distance, so it is the reciprocal of wavelength rather than wavelength itself. Use $λ$ in centimetres to obtain cm^-1."},{"text":"

Wavenumber = 1/λ
Use λ in m for cm^-1

","correct":false,"explanation":"Taking the reciprocal of a wavelength measured in metres produces m^-1, not cm^-1. For cm^-1, use $λ$ in centimetres and calculate $1/λ$."},{"text":"

Wavenumber = 2π/λ
Use λ in cm for cm^-1

","correct":false,"explanation":"The factor $2π$ belongs to angular wavenumber, not the spectroscopic wavenumber shown on ordinary IR spectra. Spectroscopic wavenumber is $1/λ$ with $λ$ in centimetres."}]},{"id":"86b6fbba-cf48-4e28-b638-faec4ecb7ab2","cardType":"cloze","points":null,"front":"Higher wavenumber means [ ] and [ ].","back":"Higher wavenumber means higher frequency and higher energy.","mcqOptions":[{"text":"Higher wavenumber means higher frequency and higher energy.","correct":true,"explanation":"Wavenumber equals frequency divided by the speed of light, so it rises with frequency. Since photon energy is $E=hν$, it also rises with energy."},{"text":"Higher wavenumber means lower frequency and higher energy.","correct":false,"explanation":"Wavenumber is directly proportional to frequency, not inversely proportional to it. Higher wavenumber therefore corresponds to higher frequency and, through $E=hν$, higher energy."},{"text":"Higher wavenumber means higher frequency and lower energy.","correct":false,"explanation":"Although frequency increases with wavenumber, energy cannot decrease because energy is directly proportional to frequency. Higher wavenumber means both higher frequency and higher energy."},{"text":"Higher wavenumber means lower frequency and lower energy.","correct":false,"explanation":"This reverses both direct relationships. Wavenumber increases with frequency, and photon energy increases with frequency, so higher wavenumber means higher frequency and higher energy."}]},{"id":"40d6edcb-02c1-475f-9014-c52af3b6ee6a","cardType":"basic","points":2,"front":"Which bonds tend to absorb at higher wavenumber?","back":"

Stronger bonds
Bonds involving lighter atoms

","mcqOptions":[{"text":"

Stronger bonds
Bonds involving lighter atoms

","correct":true,"explanation":"Stronger bonds have larger force constants, while lighter bonded atoms give smaller reduced masses. Both effects increase vibrational frequency and therefore increase absorption wavenumber."},{"text":"

Weaker bonds
Bonds involving lighter atoms

","correct":false,"explanation":"Weaker bonds have smaller force constants and therefore vibrate at lower wavenumbers. High-wavenumber absorptions generally involve stronger bonds between lighter atoms."},{"text":"

Stronger bonds
Bonds involving heavier atoms

","correct":false,"explanation":"Stronger bonds raise vibrational wavenumber, but heavier atoms increase reduced mass and lower it. Bonds that absorb higher generally are stronger and involve lighter atoms."},{"text":"

Weaker bonds
Bonds involving heavier atoms

","correct":false,"explanation":"Both trends are reversed: weaker bonds reduce the restoring force, and heavier atoms increase reduced mass. Higher-wavenumber vibrations instead involve stronger bonds and lighter atoms."}]},{"id":"4ad5b5a9-7f91-479d-ab4f-ef1e53aee939","cardType":"basic","points":1,"front":"What is plotted on the x-axis of a typical IR spectrum?","back":"Wavenumber / cm^-1.","mcqOptions":[{"text":"Wavenumber / cm^-1.","correct":true,"explanation":"IR spectra conventionally plot wavenumber on the horizontal axis. Wavenumber is measured in reciprocal centimetres and is directly proportional to the radiation’s frequency and energy."},{"text":"Transmittance / %.","correct":false,"explanation":"Transmittance is normally plotted on the vertical axis, not the horizontal axis. The x-axis shows wavenumber, measured in cm^-1, which identifies absorption positions."},{"text":"Absorbance / arbitrary units.","correct":false,"explanation":"Absorbance may be used on the vertical axis of some spectra, but it is not the usual x-axis quantity. A typical IR spectrum plots wavenumber in cm^-1 horizontally."},{"text":"Wavelength / μm.","correct":false,"explanation":"Wavelength is related inversely to wavenumber, but standard A-level IR spectra use wavenumber rather than wavelength on the x-axis. Its unit is cm^-1."}]},{"id":"b62160b1-0a1e-4c29-b3cd-24dfbba44dd8","cardType":"basic","points":1,"front":"What is plotted on the y-axis of a typical IR spectrum?","back":"Transmittance / %.","mcqOptions":[{"text":"Transmittance / %.","correct":true,"explanation":"A typical IR spectrum shows the percentage of incident infrared radiation transmitted through the sample on its vertical axis. Absorption therefore produces downward troughs in transmittance."},{"text":"Wavenumber / cm^-1.","correct":false,"explanation":"Wavenumber identifies the positions of absorptions and is plotted on the horizontal axis. The typical y-axis instead shows percentage transmittance through the sample."},{"text":"Absorbance / arbitrary units.","correct":false,"explanation":"Although some instruments can display absorbance, the typical spectrum used at A level plots percentage transmittance vertically. This is why stronger absorptions point downwards."},{"text":"Wavelength / μm.","correct":false,"explanation":"Wavelength could describe infrared radiation but is not the standard y-axis quantity. Typical IR spectra show percentage transmittance on the vertical axis and wavenumber horizontally."}]},{"id":"461d8ba2-4dd3-41de-aec4-e5a9ce84a1fb","cardType":"basic","points":2,"front":"Why does strong IR absorption appear as a downward peak?","back":"Less IR is transmitted at that wavenumber.","mcqOptions":[{"text":"Less IR is transmitted at that wavenumber.","correct":true,"explanation":"At an absorbed wavenumber, the sample removes more radiation from the incident IR beam. Less radiation reaches the detector, so percentage transmittance falls and produces a downward peak."},{"text":"More IR is transmitted at that wavenumber.","correct":false,"explanation":"Absorption does not mean that more radiation passes through the sample. Strong absorption leaves less IR transmitted at that wavenumber, causing the transmittance trace to fall."},{"text":"More IR is reflected at that wavenumber.","correct":false,"explanation":"The molecule absorbs rather than reflects the relevant IR radiation. Consequently, less IR is transmitted to the detector at that wavenumber and the transmittance curve moves downwards."},{"text":"More IR is emitted at that wavenumber.","correct":false,"explanation":"Molecular vibrations absorb selected frequencies rather than creating additional infrared radiation. Less IR is transmitted at the corresponding wavenumber, producing a downward feature on a transmittance spectrum."}]},{"id":"e03a1c40-b278-4ce8-a12d-89f9846fb8ba","cardType":"cloze","points":null,"front":"Most IR spectra have wavenumber [ ] from left to right, so higher energy is on the [ ].","back":"Most IR spectra have wavenumber decreasing from left to right, so higher energy is on the left.","mcqOptions":[{"text":"Most IR spectra have wavenumber decreasing from left to right, so higher energy is on the left.","correct":true,"explanation":"The conventional IR axis runs from high to low wavenumber as the eye moves right. Because energy is proportional to wavenumber, the highest-energy radiation is on the left."},{"text":"Most IR spectra have wavenumber increasing from left to right, so higher energy is on the right.","correct":false,"explanation":"This reverses the conventional wavenumber scale. Wavenumber decreases from left to right, and energy rises with wavenumber, so higher energy must be on the left."},{"text":"Most IR spectra have wavenumber decreasing from left to right, so higher energy is on the right.","correct":false,"explanation":"The axis direction is identified correctly, but the energy side is reversed. Since energy is directly proportional to wavenumber, the higher-energy end is on the left."},{"text":"Most IR spectra have wavenumber increasing from left to right, so higher energy is on the left.","correct":false,"explanation":"Higher energy would lie on the right only if wavenumber increased in that direction. Conventionally it decreases from left to right, placing higher energy on the left."}]},{"id":"a144c905-ba39-4e31-bbbb-1927077a3984","cardType":"cloze","points":null,"front":"The region above about [ ] is the functional group region; below it is the [ ].","back":"The region above about 1500 cm^-1 is the functional group region; below it is the fingerprint region.","mcqOptions":[{"text":"The region above about 1500 cm^-1 is the functional group region; below it is the fingerprint region.","correct":true,"explanation":"Absorptions above approximately 1500 cm^-1 are especially useful for recognising particular bonds and functional groups. The complex pattern below this boundary is called the fingerprint region."},{"text":"The region above about 1700 cm^-1 is the functional group region; below it is the fingerprint region.","correct":false,"explanation":"The boundary has been confused with a common carbonyl absorption range. The functional group region is above about 1500 cm^-1, while the lower-wavenumber section is the fingerprint region."},{"text":"The region above about 1500 cm^-1 is the functional group region; below it is the functional group region.","correct":false,"explanation":"The approximate boundary is correct, but the region below it has been misnamed. Its complicated, molecule-specific pattern is the fingerprint region, not the functional group region."},{"text":"The region above about 1000 cm^-1 is the functional group region; below it is the absorption region.","correct":false,"explanation":"This both places the boundary too low and misidentifies the lower region. The functional group region lies above roughly 1500 cm^-1; below it is the fingerprint region."}]},{"id":"99042337-f50f-424d-9934-02d0aba994a3","cardType":"cloze","points":null,"front":"A broad absorption at 3230-3550 cm^-1 suggests [ ]; a very broad 2500-3300 cm^-1 absorption suggests [ ].","back":"A broad absorption at 3230-3550 cm^-1 suggests alcohol O-H; a very broad 2500-3300 cm^-1 absorption suggests carboxylic acid O-H.","mcqOptions":[{"text":"A broad absorption at 3230-3550 cm^-1 suggests alcohol O-H; a very broad 2500-3300 cm^-1 absorption suggests carboxylic acid O-H.","correct":true,"explanation":"Hydrogen bonding broadens O-H stretching absorptions. Alcohol O-H appears around 3230-3550 cm^-1, whereas the stronger hydrogen bonding in carboxylic acids creates a much broader 2500-3300 cm^-1 band."},{"text":"A broad absorption at 3230-3550 cm^-1 suggests carboxylic acid O-H; a very broad 2500-3300 cm^-1 absorption suggests alcohol O-H.","correct":false,"explanation":"The two O-H environments have been reversed. Alcohol O-H absorbs broadly at 3230-3550 cm^-1, while carboxylic acid O-H gives the exceptionally broad 2500-3300 cm^-1 feature."},{"text":"A broad absorption at 3230-3550 cm^-1 suggests amine N-H; a very broad 2500-3300 cm^-1 absorption suggests carboxylic acid O-H.","correct":false,"explanation":"An N-H stretch can occur near this high-wavenumber region but is usually sharper than the broad alcohol band. The first feature indicates alcohol O-H; the second indicates carboxylic acid O-H."},{"text":"A broad absorption at 3230-3550 cm^-1 suggests alcohol O-H; a very broad 2500-3300 cm^-1 absorption suggests alkane C-H.","correct":false,"explanation":"C-H stretches may occur within the lower interval but do not produce its characteristically very broad band. The broad features identify alcohol O-H and carboxylic acid O-H respectively."}]},{"id":"d2d8a01f-bc17-4e93-90d6-ec148d46bc19","cardType":"cloze","points":null,"front":"A strong, sharp 1680-1750 cm^-1 absorption suggests [ ]; a sharp 2210-2260 cm^-1 absorption suggests [ ].","back":"A strong, sharp 1680-1750 cm^-1 absorption suggests C=O; a sharp 2210-2260 cm^-1 absorption suggests C≡N.","mcqOptions":[{"text":"A strong, sharp 1680-1750 cm^-1 absorption suggests C=O; a sharp 2210-2260 cm^-1 absorption suggests C≡N.","correct":true,"explanation":"The carbonyl C=O stretching vibration gives a strong, sharp absorption near 1680-1750 cm^-1. A nitrile C≡N bond absorbs sharply at the higher range of 2210-2260 cm^-1."},{"text":"A strong, sharp 1680-1750 cm^-1 absorption suggests C≡N; a sharp 2210-2260 cm^-1 absorption suggests C=O.","correct":false,"explanation":"The bond assignments have been reversed. Carbonyl C=O absorbs strongly around 1680-1750 cm^-1, while the higher-wavenumber 2210-2260 cm^-1 band indicates a nitrile C≡N bond."},{"text":"A strong, sharp 1680-1750 cm^-1 absorption suggests C=C; a sharp 2210-2260 cm^-1 absorption suggests C≡N.","correct":false,"explanation":"C=C typically absorbs around 1620-1680 cm^-1 and is often weaker than a carbonyl peak. A strong 1680-1750 cm^-1 absorption is assigned to C=O; 2210-2260 cm^-1 indicates C≡N."},{"text":"A strong, sharp 1680-1750 cm^-1 absorption suggests C=O; a sharp 2210-2260 cm^-1 absorption suggests O-H.","correct":false,"explanation":"O-H stretching produces a broad high-wavenumber absorption rather than a sharp band at 2210-2260 cm^-1. The two stated ranges identify C=O and C≡N respectively."}]},{"id":"20f073f2-da22-4d58-8ff8-bf5fc324f6d6","cardType":"cloze","points":null,"front":"An N-H absorption is usually at [ ]; a C=C absorption is usually at [ ].","back":"An N-H absorption is usually at 3300-3500 cm^-1; a C=C absorption is usually at 1620-1680 cm^-1.","mcqOptions":[{"text":"An N-H absorption is usually at 3300-3500 cm^-1; a C=C absorption is usually at 1620-1680 cm^-1.","correct":true,"explanation":"N-H stretching absorptions occur in the high-wavenumber 3300-3500 cm^-1 range. The lower-energy stretching vibration of an alkene C=C bond appears around 1620-1680 cm^-1."},{"text":"An N-H absorption is usually at 1620-1680 cm^-1; a C=C absorption is usually at 3300-3500 cm^-1.","correct":false,"explanation":"These ranges have been exchanged. N-H stretching occurs at the higher wavenumber of 3300-3500 cm^-1, whereas C=C stretching appears at 1620-1680 cm^-1."},{"text":"An N-H absorption is usually at 3300-3500 cm^-1; a C=C absorption is usually at 1680-1750 cm^-1.","correct":false,"explanation":"The N-H range is correct, but 1680-1750 cm^-1 is associated mainly with strong C=O absorption. A C=C stretch is usually found at 1620-1680 cm^-1."},{"text":"An N-H absorption is usually at 2850-3100 cm^-1; a C=C absorption is usually at 1620-1680 cm^-1.","correct":false,"explanation":"The first range is characteristic of alkane C-H stretching rather than N-H stretching. N-H absorbs around 3300-3500 cm^-1, while the C=C range given is correct."}]},{"id":"b514836b-056c-4706-91ff-d76c5970e62c","cardType":"basic","points":1,"front":"What does an absorption at 2850-2960 cm^-1 suggest?","back":"C-H in alkanes.","mcqOptions":[{"text":"C-H in alkanes.","correct":true,"explanation":"Absorptions at 2850-2960 cm^-1 are characteristic of C-H stretching vibrations in alkanes."},{"text":"O-H in alcohols.","correct":false,"explanation":"This range is not the characteristic region for O-H stretching, which is broader and occurs at higher wavenumbers. The absorption indicates C-H in alkanes."},{"text":"C=O in aldehydes.","correct":false,"explanation":"C=O stretching gives a strong absorption near 1700 cm^-1, not in this range. The absorption indicates C-H in alkanes."},{"text":"N-H in amines.","correct":false,"explanation":"N-H stretching absorptions usually occur around 3300-3500 cm^-1. The 2850-2960 cm^-1 range indicates C-H in alkanes."}]},{"id":"dd1c486b-640a-4caf-9db3-1d5a71acf2cc","cardType":"basic","points":1,"front":"What does an absorption at 1000-1300 cm^-1 suggest?","back":"C-O in alcohols, esters or acids.","mcqOptions":[{"text":"C-O in alcohols, esters or acids.","correct":true,"explanation":"The 1000-1300 cm^-1 region commonly contains C-O stretching absorptions in alcohols, esters or carboxylic acids."},{"text":"C=O in aldehydes, ketones or acids.","correct":false,"explanation":"C=O stretching produces a strong peak near 1700 cm^-1, rather than 1000-1300 cm^-1. This region suggests C-O."},{"text":"O-H in alcohols, phenols or acids.","correct":false,"explanation":"O-H stretching in alcohols is broad and occurs around 3200-3600 cm^-1. The 1000-1300 cm^-1 absorption suggests C-O."},{"text":"C-H in alkanes, alkenes or aromatics.","correct":false,"explanation":"C-H stretching absorptions occur mainly around 2850-2960 cm^-1, not in this region. The absorption indicates C-O in these oxygen-containing compounds."}]},{"id":"a749de19-595b-48bb-9106-25b747306ace","cardType":"basic","points":2,"front":"Which two IR clues suggest a carboxylic acid functional group?","back":"

Very broad O-H at 2500-3300 cm^-1
C=O absorption around 1700 cm^-1

","mcqOptions":[{"text":"

Very broad O-H at 2500-3300 cm^-1
C=O absorption around 1700 cm^-1

","correct":true,"explanation":"Carboxylic acids show both a very broad O-H absorption from 2500-3300 cm^-1 and a C=O absorption around 1700 cm^-1."},{"text":"

Broad O-H at 3200-3600 cm^-1
C-O absorption around 1100 cm^-1

","correct":false,"explanation":"An alcohol has an O-H absorption but no carbonyl absorption, so this combination does not identify a carboxylic acid. The correct clues are the very broad O-H and C=O absorptions."},{"text":"

N-H at 3300-3500 cm^-1
C=O absorption around 1700 cm^-1

","correct":false,"explanation":"An aldehyde has a C=O absorption but not the very broad carboxylic-acid O-H band. The correct combination is very broad O-H at 2500-3300 cm^-1 and C=O near 1700 cm^-1."},{"text":"

C-H at 2850-2960 cm^-1
C-O absorption around 1100 cm^-1

","correct":false,"explanation":"An ester has C=O and C-O absorptions but lacks the very broad O-H band characteristic of a carboxylic acid. Both the broad O-H and C=O clues are required."}]},{"id":"bea0049e-d041-45e3-a837-89d6b900a4e0","cardType":"basic","points":2,"front":"How is the fingerprint region used to confirm a compound’s identity?","back":"Compare the whole pattern with a reference spectrum.","mcqOptions":[{"text":"Compare the whole pattern with a reference spectrum.","correct":true,"explanation":"The fingerprint region contains a complex pattern specific to a molecule. Comparing the whole pattern with a reference spectrum provides strong confirmation of identity."},{"text":"Compare the largest peak with a reference spectrum.","correct":false,"explanation":"Matching one prominent peak cannot confirm identity because different compounds may contain the same functional group. The whole fingerprint pattern should be compared with a reference spectrum."},{"text":"Compare the total absorption with a reference spectrum.","correct":false,"explanation":"The fingerprint region is not interpreted by measuring only its overall intensity. Identification requires comparing the whole pattern with a reference spectrum."},{"text":"Compare the number of peaks with a reference spectrum.","correct":false,"explanation":"The number of peaks alone omits their precise positions and relative shapes, which make the fingerprint distinctive. The whole pattern must be compared with a reference spectrum."}]},{"id":"ce6c94ac-5e50-4407-9f96-05223a5930c2","cardType":"basic","points":2,"front":"What IR change shows propan-2-ol has oxidised to propanone?","back":"

O-H absorption disappears
C=O absorption appears

","mcqOptions":[{"text":"

O-H absorption disappears
C=O absorption appears

","correct":true,"explanation":"Oxidising propan-2-ol to propanone removes the alcohol O-H group and forms a carbonyl group, so the O-H absorption disappears and a C=O absorption appears."},{"text":"

O-H absorption disappears
C-O absorption appears

","correct":false,"explanation":"Oxidation of propan-2-ol does not produce an ester, so a C-O absorption is not the key new feature. The O-H band disappears and a C=O band appears."},{"text":"

O-H absorption becomes stronger
C=O absorption appears

","correct":false,"explanation":"The O-H absorption should disappear during oxidation, not become stronger. Formation of propanone produces a new C=O absorption instead."},{"text":"

C-H absorption disappears
C=O absorption appears

","correct":false,"explanation":"The C-H absorptions of the alkyl groups do not disappear in this oxidation. The diagnostic change is loss of O-H and appearance of C=O."}]},{"id":"84b96ef6-3cc6-4637-8ba6-b7ef0fd231d7","cardType":"basic","points":2,"front":"How do greenhouse gases increase Earth’s average temperature?","back":"They absorb Earth’s IR, retaining energy in the atmosphere.","mcqOptions":[{"text":"They absorb Earth’s IR, retaining energy in the atmosphere.","correct":true,"explanation":"Greenhouse gases absorb infrared radiation emitted by Earth and retain energy in the atmosphere, reducing the rate at which energy escapes to space."},{"text":"They absorb sunlight, retaining light in the atmosphere.","correct":false,"explanation":"Greenhouse gases do not primarily increase temperature by absorbing incoming visible light. They absorb outgoing infrared radiation and retain energy in the atmosphere."},{"text":"They convert Earth’s IR into chemical energy in the atmosphere.","correct":false,"explanation":"The key effect is not conversion of infrared into chemical energy. Greenhouse gases absorb Earth’s IR and retain energy in the atmosphere."},{"text":"They reflect Earth’s IR, sending energy back from space.","correct":false,"explanation":"Greenhouse gases do not increase temperature by reflecting infrared radiation back from space. They absorb Earth’s IR, retaining energy in the atmosphere."}]},{"id":"0f63eb35-d481-47ec-bd4a-c6a474c9bb73","cardType":"basic","points":3,"front":"Why are N₂ and O₂ poor IR absorbers but CO₂ can absorb IR?","back":"

N₂/O₂: vibrations do not change dipole.
CO₂: some vibrations change dipole.

","mcqOptions":[{"text":"

N₂/O₂: vibrations do not change dipole.
CO₂: some vibrations change dipole.

","correct":true,"explanation":"N₂ and O₂ vibrations do not change dipole, so they absorb IR poorly. Some CO₂ vibrations change dipole, allowing IR absorption."},{"text":"

N₂/O₂: vibrations change dipole.
CO₂: vibrations do not change dipole.

","correct":false,"explanation":"N₂ and O₂ are poor absorbers because their vibrations do not change dipole, not because they have changing dipoles. Some CO₂ vibrations do change dipole."},{"text":"

N₂/O₂: molecules have low mass.
CO₂: molecules have high mass.

","correct":false,"explanation":"Molecular mass does not determine whether a vibration is IR active. N₂ and O₂ lack a changing dipole during these vibrations, whereas some CO₂ vibrations have one."},{"text":"

N₂/O₂: molecules are gases.
CO₂: molecules are solids.

","correct":false,"explanation":"Both gases and solids can interact with radiation, so physical state is not the deciding factor. IR absorption depends on whether molecular vibrations change dipole."}]},{"id":"d3283020-4b6f-4026-83fc-2553c990d5a5","cardType":"basic","points":3,"front":"What is IR spectroscopy less good at determining?","back":"

Exact carbon skeleton
Number of each hydrogen type
Molecular mass

","mcqOptions":[{"text":"

Exact carbon skeleton
Number of each hydrogen type
Molecular mass

","correct":true,"explanation":"IR spectroscopy identifies functional groups but generally cannot establish the exact carbon skeleton, count each type of hydrogen, or determine molecular mass reliably."},{"text":"

Functional groups
Bond types
Presence of heteroatoms

","correct":false,"explanation":"IR spectroscopy is useful for identifying functional groups, so these are not its main limitations. Its limitations include the exact carbon skeleton, hydrogen counts and molecular mass."},{"text":"

O-H groups
C=O groups
C-O groups

","correct":false,"explanation":"IR spectroscopy can often distinguish O-H, C=O and C-O absorptions, so these functional-group observations are strengths rather than limitations. It is less good at structural detail and mass."},{"text":"

Presence of absorptions
Wavenumber of absorptions
Intensity of absorptions

","correct":false,"explanation":"The presence of absorption bands and their approximate wavenumbers are central uses of IR spectroscopy. The technique is less good at exact skeletons, hydrogen counts and molecular mass."}]}]}],"examCountdown":{"examDate":"2027-05-28","paperLabel":"Paper 1"},"heading":"Infrared spectroscopy","title":"Infrared spectroscopy Flashcards","topbar":{"backHref":"/a-level/chemistry/edexcel/flashcards"},"topicSidebar":"$L38"}]}],"topicId":"7b9d5529-da12-5a5c-9988-d7e10ad82d9b","walled":"$L39"}],"$L3a","$L3b"]