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 |
