Ch.12 IR and Mass Spec Flashcards
Infrared Spectroscopy
Measures the bond vibration frequencies in a molecule and is used to determine the functional group
Mass Spectroscopy
Fragments the molecule and measures the masses
Nuclear Magnetic Resonance
Spectroscopy detects signals from hydrogen atoms and can be used to distinguish isomers
Ultraviolet Spectroscopy
Uses electron transitions to determine bonding patterns
What is Frequency?
The number of complete wave cycles that pass a fixed point in a second
What is Wavelength ?
Is the distance between any two peaks of the wave
Frequency and wavelength are ________ proportional (Directly or Inversely)
Inversely
Higher frequency means _____ wavelength (Shorter or longer)
Shorter wavelength
For shorter wavelength means ______ frequency (Lower or higher)
Higher
For lower frequency, the wavelength is ________ (Longer or shorter)
Longer
For longer wavelength, the frequency is ______ (Lower or higher)
Lower frequency
What is the wavelength range for the IR region?
2.5 to 25 nanometers
What is a wavenumber?
The reciprocal of wavelength
What are the units of wavenumber?
1/cm
Wave numbers are proportional to what two things?
- Frequency 2. Energy
In molecular vibrations, if the bond is stretched, a restoring force pulls the two atoms __________ (Together or Apart)
Together
In molecular vibrations, if a bond is compressed, a restoring force pulls the two atoms ______ (Together or Apart)
Apart
The atoms vibrate when a bond is _____
Stretched or Compressed
Covalent bonds absorb energy according to what 3 things?
- Polarity 2. Bond strength 3. Molar mass
Frequency _______ with increasing atomic mass (increases or decreases)
Decreases
What is Spectroscopy?
An analytical technique which helps determine a structure
Frequency ______ with increasing bond energy (increases or decreases)
Increases
Nonlinear molecule with n atoms usually has _________ fundamental vibrational modes
3n-6
Can two molecules give the exact same IR?
No, except enantiomers
What is the range for simple stretching?
1600 to 3500 cm-1
What is the range for complex vibrations?
600 to 1400 cm-1
A polar bond is usually IR ______ (Active or inactive)
Active
Stronger carbon carbon bonds absorb at _______ frequencies Higher or lower
Higher frequencies
Why the stronger carbon carbon bonds absorb at higher frequencies?
Because the bond is difficult to stretch
Does conjugation in C-C bonds lower or increases the frequency?
Lowers
A greater percent of s character in the hybrid orbitals will make the C-H bond_______ (Stronger or Weaker)
Stronger
The C-H bond of an sp3 carbon will be slightly _________ than the C-H bond of an sp2 or an sp carbon (weaker or stronger)
Weaker
what is Spectroscopy?
an analytical technique which helps determine a structure
