on-line spectroscopy 1!!! Chemistry 1B Fall 2013 Chemistry 1B, Fall 2013 Lecture Spectroscopy Lectures Spectroscopy Fall 2013

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1 Lecture 190 Spectroscopy Flipping the lecture discussion Flip teaching (or flipped classroom) is a form of blended learning in which students learn new content online by watching video lectures, usually at home, and what used to be homework (assigned problems) is now done in class with teacher offering more personalized guidance and interaction with students, instead of lecturing. This is also known as backwards classroom, reverse instruction, flipping the classroom and reverse teaching. [1 online spectroscopy 1!!! Chemistry 1B Fall W 89 Lectures 190 Spectroscopy Fall this week WebAssign W8 spectroscopy problems from sample final (conceptual) due Sunday November 4 next week WebAssign W9 kinetics calculations (last WebAssign) due Wednesday December 4 5 spectroscopic principles (Chem 1M/1N exps. #6 and #11) spectroscopic excitations ( E = h = hc/ ; = c ) (nm) (sec 1 ) radiation technique molecular excitation 6 7 1

2 Lecture 190 Spectroscopy spectroscopic excitations ( E = h = hc/ ; = c ) spectroscopic excitations: ESCA (nm) (sec 1 ) radiation technique molecular excitation (nm) (sec 1 ) radiation technique molecular excitation xrays ESCA breaking of bonds (xray damage) xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons near uv UVVIS excitation of and nonbonding (n) electrons visible infrared IR vibrational excitations (IR) decreases microwave microwave ESR rotations of molecules and flipping unpaired electron spins in external magnetic field radiowave NMR (MRI) flipping of nuclear spins in an external magnetic field 8 9 ESCA ESCA photoelectric effect for inner shells Electron Spectroscopy for Chemical Analysis xrays emitted photoelectron 0 characteristic of atom type involved in bonding p s 1s h absorbed O 1s s p ESCA (and photoelectron effect) ESCA (binding is like work function for inner electrons) velocity of each electron measured Why O1s higher binding than C1s? emitted electrons from different levels binding ( ) 1 mv X ray electron h 1 binding ( ) h 1 mv X ray electron 13

3 Lecture 190 Spectroscopy spectroscopic excitations: ESCA vacuum UV (nm) (sec 1 ) radiation technique molecular excitation (nm) (sec 1 ) radiation technique molecular excitation xrays ESCA breaking of bonds (xray damage) xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons vacuum UV excitedstate orbitals in polyatomic molecules destructive interference leads to antibonding orbitals which are not usually occupied in the ground state of molecules but which may become occupied upon excitation of electrons by light types of antibonding orbitals: C 4 : * = sp 3 on C 1s on C 4 : * = sp on sp on * = p on p on energies of orbitals in double bond * * [sp on sp on ] [p on p on ] [p on p on ] [sp on sp on ] 18 s s* and s * excitations are in the far UV regrion * * * (weak) * [sp on sp on ] [p on p on ] [p on p on ] [sp on sp on ] 19 3

4 Lecture 190 Spectroscopy vacuum UV spectroscopic excitations (UVVIS) (nm) (sec 1 ) radiation technique molecular excitation (nm) (sec 1 ) radiation technique molecular excitation xrays ESCA breaking of bonds (xray damage) xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of of electrons far uv vacuum UV excitation of electrons near uv visible UVVIS excitation of and nonbonding (n) electrons 0 1 near UV transitions * * * [sp on sp on ] [p on p on ] [p on p on ] [sp on sp on ] relative on lone pair nonbonding electrons * * { n * 347nm n: nonbonded e s (higher E than in some molecules; lower E than in others) 3 summary spectroscopic excitations (UVVIS) (nm) (sec 1 ) radiation technique molecular excitation uvvis xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons near uv visible UVVIS excitation of of and nonbonding (n) (n) electrons weak adapted from:

5 Lecture 190 Spectroscopy UVVIS spectrometers (Chem 1M/1N exps. #6 and #11) why do objects appear colored? why do objects appear colored?? low electronic absorptions in the visible region of electromagnetic spectrum result in the reflection (transmission) of wavelengths of the complementary color. LUMO electronic transition OMO LUMO OMO ighest Occupied Molecular Orbital Lowest Unoccupied Molecular Orbital 6 absorbs photon of hn =E LUMO E OMO 7 Br (g), I (g), NO closely spaced OMO and LUMO due to dorbital m.o.s or open shells (unpaired e s) transition metal complex ions octahedral complex t g e g (lonepair) n * * in molecules with conjugated pisystems END OF SPECTROSCOPY 1 AND onto more spectroscopy!!! rhodopsin, the molecule most important to seeing color 8 9 spectroscopic excitations (nm) (sec 1 ) radiation technique molecular excitation online spectroscopy!!! Chemistry 1B Fall xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons near uv UVVIS excitation of and nonbonding (n) electrons visible infrared IR vibrational excitations (IR)

6 10 Chemistry 1B, Fall 013 Lecture 190 Spectroscopy diatomic molecules (vibrating and rotating) vibrations new unit wave number 1 cm c cm 10 1 E hc c cm sec larger higher photon larger higher vibration vibrational frequencies of homonuclear diatomic molecules and ions vibrational motion in molecules ( O) wave number larger higher photon vibrational frequency ( ) depends on mass of atoms (lighter ï higher ) strength of bond (tighter spring ï higher ) wave number 1 1 cm cm 1 E hc c cm sec Molecule Bond Order Vibrational frequency (cm 1 ) Li C 1781 N N.5 07 O 1580 O F low mass vibrational frequency follows bond order greater b.o. î greater frequency ORIGINALLY FROM: b.o vibrational motions in molecules (benzene) IR spectrometer breathing (stretching) mode asymmetric stretching mode Chubby Checkers twisting mode American Bandstand Movies provided courtesy: timro@hydrogen.cchem.berkeley.edu

7 Lecture 190 Spectroscopy infrared vibrational spectrocopy (fig ) photons at infrared wavelengths excite the vibrational motion of atoms in a molecule group frequencies different types of bonds require different photons for vibrational excitation a given bond type will have a similar absorption in various molecules Bond Characteristic Frequency (approximate) (nm) υ (cm 1 ) [E hcυ] ~ C C C = C C C C O C = O C O note to excite bond vibration: E CC > E C=C > E CC 39 IR spectra spectroscopic excitations NO O (nm) (sec 1 ) radiation technique molecular excitation C ~300 cm xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons NO C=O C=O ~1700 cm near uv visible UVVIS excitation of and nonbonding (n) electrons infrared IR vibrational excitations (IR) O ~3600 cm microwave microwave ESR rotations of molecules and flipping unpaired electron spins in external magnetic field radiowave NMR (MRI) spectrometers (nm) (sec 1 ) radiation technique molecular excitation xrays ESCA breaking of bonds (xray damage) far uv vacuum UV excitation of electrons near uv visible UVVIS excitation of and nonbonding (n) electrons infrared IR vibrational excitations (IR) microwave microwave ESR rotations of molecules and flipping unpaired electron spins in external magnetic field radiowave NMR (MRI) flipping of nuclear spins in an external magnetic field

8 Lecture 190 Spectroscopy NMR WY? protons (hydrogen nuclei), like electrons, behave as if they were tiny magnets identifying equivalent and nonequivalent protons to flip hydrogen atoms (nuclei) in different chemical environments requires slightly different energies (chemical shift) in an external magnetic field, spin up and spin down will have different energies (all equivalent, ClC 1 peak one chemical shift ) in NMR spectroscopy, photons in the radiowave region have the correct to cause a hydrogen nucleus to flip its spin (two environments, Cl C and C 3 peaks two chemical shifts ) vocabulary: fluorescence not responsible for spinspin coupling (pp ) will get plenty in ochem fluorescence emission of radiation (almost) directly from the excited state excited photon E in =h in ground ( out in ) ( out in ) photon Eout =h out 46 time ~ 10 1 to 10 9 sec (fluorescence stops soon after exciting light is turned off) 47 vocabulary: radiationless decay (nonradiative decay) phosphorescence radiationless decay transition from a higher to a lower state with a loss of in the form of heat rather than emission of a photon phosphorescence slow return to ground state by emission of photon from intermediate state excited photon excited radiationless decay photon E in =h in intermediate state photon E in =h in ground thermal ground ( out < in ) ( out > in ) E out =h out 48 time ~ 10 3 to 10 sec and longer (phosphorescence continues after exciting light is turned off) 49 8

9 Lecture 190 Spectroscopy chemiluminescence chemiluminescence: fireflies chemiluminescence light given off when chemical reaction leaves products in excited states and then the product fluoresces A B C* C light molecule C in excited state chemiluminescence: fireflies chemiluminescence: light sticks bioluminescence Bioluminescence: Explanation for Glowing Seas Suggested END OF SPECTROSCOPY AND onto kinetics!!! According to the study, here is how the lightgenerating process in dinoflagellates may work: As dinoflagellates float, mechanical stimulation generated by the movement of surrounding water sends electrical impulses around an internal compartment within the organism, called a vacuolewhich holds an abundance of protons. These electrical impulses open socalled voltagesensitive proton channels that connect the vacuole to tiny pockets dotting the vacuole membrane, known as scintillons. Once opened, the voltagesensitive proton channels may funnel protons from the vacuole into the scintillons. Protons entering the scintillons then activate luciferase a protein, which produces flashes of light, that is stored in scintillons. Flashes of light produced by resulting luciferase activation would be most visible during blooms of dinoflagellates

10 Lecture 190 Spectroscopy colored transition metal complexes glazes end of lectures on spectroscopy Ni(N 3 ) 6 Br CoCl 6 O NiSO 4 6 O dorbitals and ligand Interaction (octahedral field) absorption of visible light in octahedral transition metal complexes e g O Ni(N 3 ) 6 Cl [Ni(N 3 ) 6 ] (aq) Cl (aq) 3d Ni [Ar]3d 8 dorbitals pointing directly at axis are affected most by electrostatic interaction dorbitals not pointing directly at axis are least affected (stabilized) by electrostatic interaction 58 ibchem.com/ib/ibfiles/periodicity/per_ppt/crystal_field_theory.ppt [Ni(N 3 ) 6 ] 3d orbitals all have same in Ni (g) presence of 6N 3 cause splitting of the energies of the 3dorbitals into two levels in [Ni(N 3 ) 6 ] visible light causes electronic transitions between the two levels resulting in colored transition metal complexes t g 59 ß carotene; conjugated double bonds (figure 14.56, 14.57) rhodopsin (11cis retinal opsin) intradiscal (lumen) 11cis retinal opsin (protein) 60 interdiscal (cytoplasmic) 61 10

11 Lecture 190 Spectroscopy how do we see color??? AA! that s what its all about 6 63 signal amplification in visual excitation cascade cytoplasmic tail FROM: Advanced (don t Fret) photonî10 6 Na Visual transduction cascade, amplification 1 photon 1 Rh* ~00 T* 1 T* 1 PDE 1 PDET*GDP many cgmp many GMP closes 00 Na channels 10 6 Na ions 66 11