Functional Groups Answers – Flashcards
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Alkyl, and occasionally aryl (aromatic) functions are represented by the R- Methyl: CH3– Ethyl: CH3CH2– Propyl: CH3CH2CH2– Isopropyl: (CH3)2CH– Phenyl: C6H5– etc. |
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[image] |
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Br : MS |
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M+2 peak is nearly as tall as m peak |
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Cl : MS |
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M+2 peak is 1/3 of the size of M+ peak |
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N : MS |
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has an odd # for their M+ peaks |
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IR: high energy |
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high frequency large wave# short wave lengths |
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intensity of bond |
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greater the charge in the dipole moment, more intense the absorption -more polar the bond, the more intense it is |
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IR characteristics |
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-cant determine structure alone -some signals are ambiguous -if there is an absence of a signal, thats definite proof that the function roups is absent -look at the literature value of the compound to confirm or vice versa |
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triplanar: degrees? |
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120 degress |
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linear: bond angle? |
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109.5 degrees |
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linear: bond angle? |
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180 degrees |
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C-C :bond length? |
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1.54 A |
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C=C: bond length? |
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1.34 A |
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C=-C: bond length? |
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1.20 A |
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condensed formula |
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CH3OCH3 |
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acid strength: down group |
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larger size differnce, weaker bond |
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acid strength: across row |
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greater electronegativity, more polorized bond |
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acid strength: c-H vs C-O |
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conjugate base is stablized by inductive and resonance effects |
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acid strength: molecular weight |
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conjugate base is better stablized by inductive effects |
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stronger bases than -OH put in water |
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leveling effect -bases stronger than OH- will simply deprotonate water to form the weaker base OH- |
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molecular weight |
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what is the main piece of information sought from analysis of a compound by low-resolution mass spectrometry? |
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molecular formula |
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What is the main piece of information sought from analysis of a compound by high resolution mass spectometry? |
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identification of functional groups |
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What is the main piece of information sought form analysis of a compound by infrared spectroscopy? |
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-hexane has a higher molecular weight and more van der waals interactions |
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higher BP: hexane vs pentane? |
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-alcohol can hydrogen bond to its neighbors |
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higher BP: ether vs alcohol |
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1. ion charges 2. higher molecular weight 3. has halogen |
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most soluable in water? |
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-more symmetrical |
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most inportant factor for higher MP? |
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1. ion-ion, coulombic attraction 2. dipole-dipole attraction 3. hydrogen bond - typeof dipole-dipole 4. van der waals -transient dipole-dipole |
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explain 4 differnt types of bonds |
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a gas chromotograph and a mass spectrometer |
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what two instruments are coupled together in a so-called GC-MS? |
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compounds with ane ven # of nitrogenn (or O) have an even molecular mass compounds with an odd # of nitrogems have an odd molecular mass |
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explain what the nitrogen rule is |
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the stretch produces no charge in the dipole moment |
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why cant the symmetrical stretch of carbon dioxide produce a peak (absorption) in a normal IR spectrum? |
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H2O has a greater propensity to donate a proton because the conjugate base (OH-) would be more stable than (NH2-) due to the more electronegative oxygen atom |
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which one is the stronger acid and why? H2O vs NH3 |
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CH3CF2COOH has a greater propensity to donate a proton because the conjugate base is more stable as a result of the more effective (-) charge delocalization due to stronger induction thru the sigma bonds by the more proximal F atoms |
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which one is the stronger acid? F2CHCH2COOH vs CH3CF2COOH |
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HCl has a greater propensity to donate a proton becaus the conjugate base (Cl-) would be more stable than (F-) due to Cl- being larger and the negative charge being dispersed over a larger volume |
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which one is the stronger acid? HF vs HCl |
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CH=-CH has agreater propensity to donate a proton because the conjugate base is more stable as a result of the lone pair residing in an sp orbital (as opposed to an sp3 orbital) which has more s character (50%), so the lone pair is in a lower energy, closer to the nucleus |
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which is the stronger acid? CH3CH3 vs CH=-CH |
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pie bonds and heteroatoms |
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in general, what are two structural features in organic compounds, any one of which, that give rise to so-called functional groups and useful reactivity? |
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electromagnetic radiation |
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radient energy having dual properties of both waves anad particles |
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photons |
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particles of electromagnetic readiation |
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quantum |
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each photon has a discrete amount of energy |
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wavelength and frequency |
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electrommagnetic radiation can be characterized by its: |
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wavelength |
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the distance form one point on a wave to the same point on an adjacent wave |
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frequency |
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the number of waves passing per unit of time, hertz |
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true |
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t/F? for absorption ot occur, the energy of the photon must match the difference between two energy states in a molecule |
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IR radiation |
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the energy source used in IR spectroscopy |
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true |
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t/f? absorption of IR light causes changes in the vibrational motions of a molecule |
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true |
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t/f? IR spectroscopy distinguishes between the different kinds of bonds in a molecule, so it is possible to determine the functional groups present |
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1. light passes through a sample 3. frequencies that match the vibrational frequencies are absorbed,and the remaining light is transmitted to a detector 3. an "IR spectrum is a plot of the amount of transmitted light versus its wavenumber |
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characteristics of IR: |
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100% transmittance |
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that all the light shone on a sample is transmitted and none is absorbed |
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0% transmittance |
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that none of the light shone on the sample is transmitted and all is absorbed |
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true |
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t/f? stronger bonds vibrate at a higher frequency, so they absorb at higher wavenumbers |
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. |
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bonds with lighter atoms vibrate at higher frequency, so they absorb at higher wavenumbers |
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. |
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the higher the percent s-character, the stronger the bond and the hgiher the wavenumber of absorption |
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. |
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for a bond to absorb in the IR, there must be a change in dipole moment during the vibration |
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IR inactive |
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symmetrical nonpolar bonds do not absorb in the IR |
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. |
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IR spectroscopy is often used to determine the outcome of a chemical reaction |
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. |
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i a mass spectrometer, a molecule is vaporized and ionized by bombardment with a beam ofhigh-energy electrons |
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. |
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the electron beam ionizes the molecule by causing it to eject an electron |
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radical cation, M+ |
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when the elctron beam is ionized the molecule, the species that is formed is called? |
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. |
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the mass of M+ represents the molecular weight of M |
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. |
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because M is unstable, it decomposes to fomr fragments of radicaals and cations that have a lower molecular weight than M+ |
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. |
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the mass spectrum analyzes the masses of cations, a plot of the amount of each cation versus its mass to charge ratio |
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. |
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when the sample is injected into the GC, it is vaporized and swept by an inert gas through the column and components are usually seperated by boiling points |