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Questions and Answers
What is the term used for the region below 1500 cm-1 in an IR spectrum?
What is the term used for the region below 1500 cm-1 in an IR spectrum?
Which of these gases is known for absorbing infrared light and contributing to the greenhouse effect?
Which of these gases is known for absorbing infrared light and contributing to the greenhouse effect?
What can be determined using the specific wavenumbers in IR Spectra?
What can be determined using the specific wavenumbers in IR Spectra?
Which of the following compounds would be expected to have a broad peak around 3200-3600 cm-1 in an IR spectrum?
Which of the following compounds would be expected to have a broad peak around 3200-3600 cm-1 in an IR spectrum?
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Which peak is significant in identifying organic molecules in the fingerprint region?
Which peak is significant in identifying organic molecules in the fingerprint region?
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Which molecular geometry corresponds to a bond angle of approximately $120^{ ext{o}}$ and has three bonded atoms?
Which molecular geometry corresponds to a bond angle of approximately $120^{ ext{o}}$ and has three bonded atoms?
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What is the bond angle in a tetrahedral molecular geometry?
What is the bond angle in a tetrahedral molecular geometry?
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In infrared spectroscopy, what is the term used for the absorption of energy that matches the natural frequencies of covalent bonds?
In infrared spectroscopy, what is the term used for the absorption of energy that matches the natural frequencies of covalent bonds?
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Which molecular geometry is characterized by a bond angle of $90^{ ext{o}}$ and has six bonded atoms?
Which molecular geometry is characterized by a bond angle of $90^{ ext{o}}$ and has six bonded atoms?
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What is the bond angle for a bent molecular geometry with two bonded pairs and one lone pair?
What is the bond angle for a bent molecular geometry with two bonded pairs and one lone pair?
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Which type of molecular geometry has five bonded atoms and a bond angle of $90^{ ext{o}}$?
Which type of molecular geometry has five bonded atoms and a bond angle of $90^{ ext{o}}$?
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How many lone pairs are present in a trigonal bipyramidal molecular geometry?
How many lone pairs are present in a trigonal bipyramidal molecular geometry?
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A molecule with a square planar geometry will most likely have how many bonded atoms?
A molecule with a square planar geometry will most likely have how many bonded atoms?
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Study Notes
Infrared Spectroscopy
- Infrared spectroscopy identifies molecules by analyzing their absorption of infrared light.
- Covalent bonds vibrate at specific frequencies when absorbing this energy.
- The absorption of energy matches natural frequencies, called resonance.
- Vibrations can be symmetric or asymmetric stretches or bends.
Molecular Geometry
- Linear: 2 bonding pairs, 180° bond angles
- Trigonal Planar: 3 bonding pairs, 120° bond angles
- V-Shape (Bent): 2 bonding pairs, <120° bond angles
- Tetrahedral: 4 bonding pairs, ~109.5° bond angles
- Trigonal Bipyramidal: 5 bonding pairs, ~90°, 120° bond angles
- See-Saw: 4 bonding pairs, 1 <120°, 1 <90° bond angles
- T-Shape: 3 bonding pairs, 1 <180°, 1 <90° bond angles
- Octahedral: 6 bonding pairs, 90° bond angles
- Square Pyramidal: 5 bonding pairs, <90° bond angles
- Square Planar: 4 bonding pairs, 90° bond angles
Mass Spectrometry
- Mass spectrometry analyzes the molar mass and identifies isotopes.
- The most intense peak in mass spectra is from the stable isotopes.
- Breaking a bond to determine the location is a key technique to evaluate the structure.
Identifying Functional Groups using IR Spectra
- IR spectra use wavenumbers (reciprocal of wavelength) to identify bonds.
- Specific wavenumber ranges correspond to specific functional groups (e.g., alcohols, aldehydes, ketones, carboxylic acids).
Functional Groups and Characteristic Absorption Ranges
- C-O : Hydroxy, Ester: 1040-1300 cm-1
- C=C : Aromatic compound, alkene: 1500-1680 cm-1
- C=O: Amide carbonyl, carboxyl, ester: 1640-1690, 1670-1740, 1710-1750 cm-1
- C≡N : Nitrile: 2200-2250 cm-1
- C-H: Alkane: 2850-2950 cm-1
- N-H: Amine, amide: 3300-3500 cm-1
- O-H: Carboxyl, hydroxyl: 2500-3000, 3200-3600 cm-1
Identifying Molecules from IR Spectra
- Comparing IR spectra of different compounds helps identify propan-2-ol and propanone isomers.
- Different functional groups absorb infrared light at different frequencies.
Fingerprint Region
- The region below 1500 cm-1 is referred to as the fingerprint region.
- The fingerprint region is unique for each molecule.
- It's due to complex interactions among all bonds.
Identifying Molecules from IR Spectra with Specific examples
- IR spectra can distinguish propan-1-ol, propanal, and propanoic acid molecules by recognizing the characteristic peaks for OH, carbonyl (C=O), and C-H bonds.
- OH peaks tend to be broad, C=O peaks tend to be sharp. C-H peaks are wiggles.
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Description
Test your knowledge on infrared spectroscopy, molecular geometry, and mass spectrometry. Dive into the specifics of molecular vibrations, bond angles, and mass analysis. This quiz encompasses key concepts you'll need to master in chemistry.
