lect29-apr14-1

lect29-apr14-1 - Chemistry 101-501 Spring 2010 Instructor:...

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Unformatted text preview: Chemistry 101-501 Spring 2010 Instructor: Dr. David P. Barondeau Office: Interdisciplinary Life Science Building Room 1196A Phone: 458-0735 E-mail: barondeau@tamu.edu (please put CHEM 101 in subject line) Lecture: MWF 9:10-10:00 Room 100 Heldenfels Office Hours: M 10:15 - 11:30 (Room 104A Heldenfels) W 10:15 - 11:30 (Room 104A Heldenfels) or by appointment Course Website: Blackboard Vista (http://elearning.tamu.edu/) Instructor Assistant: Jessica Garber jgarber@mail.chem.tamu.edu (Tues 7-9 Held 100) Supplemental Instructional Leader: Kathy Webb kmwebb2010@neo.tamu.edu 1 (Sun 9-10; Wed 7-8; Thurs 6-7 all in HRBB 15) Chemistry 101 • • • Homework problem set 7 has been assigned (due April 25th) Extra credit problems have also been assigned (due April 17th) If you are having difficulty with the homework – – – – – Email: jgarber@mail.chem.tamu.edu (IA Jessica Garber) Email me at barondeau@tamu.edu My office hours M, W 10:15 to 11:30 (HELD 104A) or by appointment Additional office hours T 4-5:00 in ILSB; R 2:45-3:45 in ILSB TA Help desk HELD 116 SI Leader Kathy Webb kmwebb2010@neo.tamu.edu Sun 9-10; Wed 7-8; Thurs 6-7 all in HRBB 15 Instructional Assistant Jessica Garber jgarber@mail.chem.tamu.edu • Review sessions – – – Tues 7-9 HELD 100 2 Molecular Orbital (MO) Theory •According to MO theory, which of the following species would be likely to exist? •H22-, Li22-, Be2, Be22- 3 Molecular Orbital (MO) Theory According to MO theory, which of the following species would have the highest bond order? F2, F22+, C22-, Li2, B22+ 4 Molecular Orbital (MO) Theory According to MO theory, which of the following species would be paramagnetic? F2, O2, N2, NO 5 Molecular Orbital (MO) Theory According to MO theory, what is the molecular orbital configuration for F2, O2, N2, N22+ 6 Chapter 10 Carbon: More than just another element ORGANIC CHEMISTRY 7 Chapter 10 Carbon: More than just another element What features of carbon lead to the abundance and What complexity of organic compounds? complexity – Stability and structural diversity – Carbon-carbon bond energy 346 kJ/mol – Carbon-hydrogen bond energy 413 kJ/mol Structural diversity – – – Carbon has four electrons in its outer shell Carbon will form four bonds to reach an octet configuration In contrast, boron and nitrogen will form three bonds in In molecular compounds molecular – Oxygen forms two bonds – Hydrogen and the halogens from one bond – Large number of bonds provides opportunity for more Large complex structures complex 8 Chapter 10 Carbon: More than just another element Carbon atom can reach an octet of electrons in Carbon a various ways various – By forming four single bonds By • Can be to either other elements or to other carbon atoms • Example: methane CH4 – By forming a double bond and two single bonds • Example: the carbon atoms in ethylene H2C=CH2 – By forming two double bonds By • Example: carbon dioxide O=C=O – By forming a triple bond and a single bond By • Example: acetylene HC≡ CH 9 Chapter 10 Carbon: More than just another element What is the hybridization for the carbon atoms in these What compounds? 10 Writing formulas and drawing structures • Molecular formula – Gives information on composition – Example: CH4 or C2H6 • Condensed formula – Gives some information on the way atoms are Gives connected connected – Example: CH3CH3 (or H3CCH3) for ethane • Structural formula – Defines how atoms are connected – Fails to describe shapes – Lewis structure 11 Writing formulas and drawing structures • Perspective drawing – Used to convey three-dimensional nature of molecules – Bonds extending out of the plane of paper represented with wedges – Bonds behind the paper as dashed wedges – Lewis structure • Ball-and-stick and space-filling models 12 Isomers • Isomers have identical composition but different structures different • Two forms of isomerism – Constitutional (or structural) – Stereoisomerism • Constitutional or structural isomers – Same empirical formula but different atom-to-atom Same connections connections • Stereoisomerism – Same atom-to-atom connections but different Same arrangement in space arrangement 13 Structural isomers 14 Stereoisomers: geometric Geometric isomers – Can occur when there is a C=C double bond – Have different physical properties (melting point, boiling point, …) – A cis isomer contains two identical groups on the same side of the double bond – A trans isomer contains two identical groups on opposite sides of the double bond Cis-2-butene Trans-2-butene 15 Stereoisomers: optical • Optical isomers – – – – molecules with non-superimposable mirror images Such molecules are called CHIRAL Such CHIRAL Pairs of chiral molecules are enantiomers Pairs enantiomers Pure samples of enantiomers have the same Pure physical properties (melting point, boiling point, etc.) etc.) – Chiral molecules in solution can rotate the plane of Chiral plane polarized light plane – The two enantiomers rotate polarized light to an The equal extent, but in opposite directions equal 16 Chiral Compounds—Polarized Polarized Light Light 17 Stereoisomers: optical Chirality generally Chirality occurs when a C atom has 4 different groups attached attached Lactic acid 18 Stereoisomers: optical Lactic acid Lactic isomers are nonsuperimposable nonsuperimposable 19 Chirality: Handedness in Chirality: Nature Nature These molecules are non-superimposable These mirror images 20 Chirality: Handedness in Chirality: Nature Nature These amino acids are non-superimposable These mirror images 21 Stereoisomers in Nature Right- and lefthanded seashells The DNA here is The right-handed right-handed 22 The egg cases of the The whelk have a rightwhelk handed twist handed 23 Life is based on chiral molecules Biosynthetic processes almost always produce pure Biosynthetic stereoisomers stereoisomers Diagnostic test for extraterrestrial life: Is there net optical Diagnostic activity (and hence produced biosynthetically) activity Many drugs are synthesized as racemic (both chiral forms) Many mixtures mixtures One enantiomer is biological One active, other is often inert active, Sometimes inactive enantiomer Sometimes has unanticipated effects has 24 Chiral molecules Thalidomide was chiefly sold Thalidomide and prescribed during the late 1950s and early 1960s to pregnant women to combat morning sickness and as an aid to help them sleep to From 1956 to 1962, From approximately 10,000 children were born with severe malformities malformities 25 ...
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