Session Start: Wed Jun 10 12:43:50 2009 Session Ident: #Chemistry [12:43] * Now talking in #Chemistry [12:43] * chemistry.gravitywaves.com sets mode: +nt [12:43] * Disconnected Session Close: Wed Jun 10 12:43:56 2009 Session Start: Mon Jun 15 07:17:58 2009 Session Ident: #Chemistry [07:17] * Now talking in #Chemistry [07:17] * chemistry.gravitywaves.com sets mode: +nt [09:01] * freddy has joined #Chemistry [09:03] * DrMasoud has joined #Chemistry [09:04] hello [09:04] hello [09:04] Welcome to chem.302 [09:04] * DrMasoud has quit IRC (Quit: Leaving) [09:04] * DrMasoud has joined #Chemistry [09:04] * DrMasoud has quit IRC [09:05] * DrMasoud has joined #Chemistry [09:05] hello [09:05] welcome to chem. 302 [09:06] * DrMasoud has quit IRC (Quit: Leaving) [09:07] * DrMasoud has joined #Chemistry [09:08] hello [09:08] * DrMasoud has quit IRC (Quit: Leaving) [09:40] * gk has joined #Chemistry [09:42] * gk has quit IRC (Quit: Leaving) [09:50] * Jicra has joined #Chemistry [09:53] * Makala has joined #Chemistry [09:54] * Michele has joined #Chemistry [09:54] * Shelley has joined #Chemistry [09:57] * Spike has joined #Chemistry [09:59] * KevinE has joined #Chemistry [10:00] * DrMasoud has joined #Chemistry [10:00] hello [10:00] * DrSturm has joined #Chemistry [10:00] * gk has joined #Chemistry [10:01] Hi Lida, today i see you fine, you might want to stay for awhile and see how things work. [10:01] * nicole has joined #Chemistry [10:01] Sure, Iam glad that things ARE WORKING [10:02] I used firefox [10:02] First are there any questions about Exam 2? [10:03] * marygrace has joined #Chemistry [10:03] On exam 2 questions 18.-23. are a good example of how most of Exams 3, 4 and the Final will look [10:03] i.e. reactions...... [10:03] * bn has joined #Chemistry [10:04] So any questions on Exam 2? Questions 18-25 are a good example of how the better part of Exams 3, 4 and the Final will look. [10:05] Answers to the work sheets can now be found on-line as .pdf files in the "Organic Chemistry I, CHE 300, Summer 2009" link [10:05] Thank you! [10:05] This way you don't have to look at the answers before you complete the work sheet..... [10:07] So IUPAC Priority List: 1. alcohol (-OH); 2, Alkene -C=C-); 3. Halide (-X); 4. Alkyl [10:07] So alcohol is still number 1 and alkenes will now be #2 [10:07] * Bre has joined #Chemistry [10:08] We need to worry about Geomteric isomers when naming alkenes, Slide #3 [10:08] When the -CH3 groups are on the same side it is "cis"; opposite sides is "trans" [10:09] Not all alkenes have geometric isomerism, slide #4 [10:09] In the C=C bond the carbons are called "vinyl" carbons [10:10] notice if one of the vinyl carbons has two of the same thing either H or alkyl groups attached to it there can not be any geometric isomerism [10:10] We will use the E/Z system for naming alkenes [10:11] Slide #6, Z meaning same side and E opposite sides [10:11] So cis/trans won't be used for anything? [10:11] So looking at Slide #7, what I do is split the double bond in half then look at each side [10:12] then assign priorities to the groups attached to each individual vinyl carbon [10:12] so for the first example there is a methyl and a hydrogen [10:12] the methyl is #1, hydrogen #2 [10:12] now the other vinyl carbon, ethyl is #1 and methyl is #2 [10:13] * nikky has joined #Chemistry [10:13] that means both of the #1 groups are on the same side so "Z" [10:14] second example first vinyl carbon methyl #1, hydrogen #2 [10:14] * jicra1 has joined #Chemistry [10:14] second vinyl carbon Br #1 (atomic number) and Cl #2 [10:14] so the #1's are on opposite sides so "E" [10:15] Now let's try a couple.... [10:15] CH3CH2CH=CHCH2CH3, when you draw this put both "H's" on one side of the double bond [10:15] * gk has quit IRC (Remote host closed the connection) [10:16] so find the longest continuous carbon chain, name the alkane, drop the "ane" and add "ene" [10:17] (Z)-3-hexene? [10:17] (Z)-3-hexene? [10:17] That is correct [10:18] (z) 3-hexene [10:18] You may see cis/tran some places in the notes, in the book or in the homework but if asked to name something on the exam where there is geometric isomerism use the E/Z system [10:19] you must have all of the dashes, (Z)-3-hexene [10:19] ok [10:19] Remember nomenclature is veru "exact" [10:19] ok [10:19] Now another [10:20] CH3CH=CHCH(CH3)2 draw this one with the "H's" on opposite sides of the C=C [10:21] (E)-4-methyl-2-pentene [10:21] (E)-4-methyl-2-pentene [10:22] i agree [10:22] That is correct [10:22] (E)-4-methyl-2-pentene [10:23] One more, CH3CH(OH)CH=CH2 [10:24] Notice no geometric isomerism possible, so no E/Z needed [10:24] 3-buten-2-ol? [10:25] yes, 3-buten-2-ol, so the alcohol, -OH, is higher priority than the C=C [10:25] 2-methyl-2-buten-1-ol [10:25] there are only 4 carbons in the compound [10:26] draw 2-mehtyl-2-buten-1-ol, and you will see it is different [10:26] o i miss counted sorry [10:26] Any questions on nomenclature? [10:27] On to slide #13, synthesis [10:28] so we can make alkenes in three ways, the dehalogenation of a vicinal dihalide is not very useful but you should be familiar with the reaction, Slide #14 [10:29] The primary way to make alkenes is via dehydrohalogenation of alkyl halides [10:29] Slide #15 notice it requires a strong base so KOH (alc) or NaOH (alc) [10:30] Can we just use KOH for all of them or would we need to use NaOH at another time? [10:30] there are no rearrangements but there may be mixtures the rate is dependent on both the alkyl halide and the base [10:30] it will be either KOH (alc) or NaOH (alc) [10:31] This is the E2 mechanism, a one step process with the base removing a hydrogen as the leaving group leaves [10:32] Slide #18 notice there are two possible products for 2-bromobutane [10:32] You will need to be able to predict which is the major product but not the actual percentages [10:32] when using KOH and NaOH it will always be E2 correct? [10:33] We will discuss that in a few minutes [10:33] Slide #21 is about Saytzeff's rule [10:33] which basically says the more substituted C=C will always be the major product [10:34] so we can tell that the products of 2-bromobutane the 2-butene will be the major product [10:35] Slide #22 again we can predict the major products based on Saytzeff's rule [10:36] Now what you need to do is get used to drawing all of the possible elimination products given any alkyl halide reacted with KOH (alc) or NaOH (alc) [10:36] So let's do some.... [10:36] CH3C(Br)(CH3)2 + KOH (alc) [10:37] CH3CH(CH3)CH2Br + KOH (alc) [10:37] CH3(CH2)3CH2Br + KOH (alc) [10:38] CH3CH2CH2CH(Br)CH3 + KOH (alc) [10:38] CH3CH2CH(Br)CH2CH3 + KOH (alc) [10:44] Need more time? [10:44] on the third one....it is supposed to be CH3 in the beginning? [10:44] Yes [10:45] I'm having trouble drawing that third one with the (CH2)3 part... [10:45] -CH2CH2CH2- [10:45] oops :) [10:48] H2C=C(CH3)2; (CH3)2C=CH2; CH3CH2CH2CH=CH2; CH3CH2CH=CHCH3 (Major) + CH3CH2CH2CH=CH2; CH3CH=CHCH2CH3 [10:48] Make sure your answers match, any questions? [10:49] what is the product on number 2? [10:49] (CH3)2C=CH2 [10:50] what is the product on number 3? [10:51] So we can also have elimination via an E1 mechanism, two steps, Slide #24 [10:51] All the products were listed [10:51] the problem with E1 just like SN1 is carbocations which can rearrange.... [10:52] Now for work sheet Chapter 8 #3. The rules..... [10:52] ok sorry [10:52] You can get out that work sheets and list the following: [10:53] 1. KOH or NaOH in alcohol will always give elimination (E2), Saytzeff's rule [10:54] 2. Other strong bases, NaOCH3 or NaOCH2CH3 will give substitution (SN2) with a CH3X and primary alkyl halide and elimination (E2) with secondary and tertiary alkyl halides [10:55] 3. Weak base, i.e. dilute -OH, will give BOTH substitution (SN1) and Elimination (E1) with secondary and tertiary alkyl halides [10:55] Slide #30 are examples [10:56] * Jicra2 has joined #Chemistry [10:56] This will be very clear on the exam, and should be in the assigned homework problems as well. [10:56] The third method to make alkenes is to dehydrate an alcohol [10:56] Slide #32 [10:57] Notice in the mechanism, Slide #33, step 2 carbocations....so watch for rearrangements [10:58] Slide #34, 1-butanol will form a primary carbocation that will rearrange [10:59] so (slide #35) better to first make the lakyl halide then use KOH or NaOH in alcohol to go with the E2 mechanism [11:00] Now for reactions of Alkenes, notice there are 15 of them, this is a good time to use the index cards..... [11:01] Looking at the study guide the mechanism you may be asked to draw for Exam 3 are E1, E2 and the Addition of HX [11:02] I want to say a couple of words about slide #15 and Slide #19 from the "Reactions of Alkenes" presentation (Chapter 9) [11:03] and that's it [11:03] Everyone should open that [11:03] For the mechanisms for Exam 3 yes, E1, E2 and Addition of HX [11:04] but we will see in a moment that even though i will not necessarily ask you to draw a mechanism you must always keep them in mind [11:05] You need to quickly understand Markovnikov's rule [11:06] do we need mechanism for anti markovnikov [11:06] That is the addition of any acid to an alkene the "H" (electrophile) will go to the vinyl carbon that already has the greater number of hydrogens [11:06] This will allow you to predict products for most of the reactions of alkenes [11:07] The general mechanism, Slide #19 [11:08] but we won't need to draw it [11:08] Step one the electrophile will add to the vinyl carbon that already has the greatest number of hydrogens attached to it [11:08] Step 2 the nucleophile adds to the other vinyl carbon [11:09] Slide #21, real example using HBr [11:10] The "H" adds to the vinyl carbon that has two hydrogens on it thus forming the more stable secondary carbocation [11:10] the Br adds the the other vinyl carbon [11:11] * DrMasoud has quit IRC (Quit: Leaving) [11:11] So now as you begin to look through all of the reactions you can apply Markovnikov and Anti-Markovnikov (electrophile goes to vinyl carbon with least number of hydrogens) to each case [11:12] Also remember that in the general addition mechanism we are forming carbocations so always watch for rearrangements [11:12] most of them are Markovnikov though, as opposed to anti-M? [11:12] So for example on my index card for the Addition of Water i would have Markovnikov orientation, watch for carbocations [11:13] For HBr or HCl with peroxides, Ani-Markovnikov etc...... [11:13] Remember you will always be asked to "apply" your knowledge [11:14] Meaning you won't see general examples using "R" but actual molecules [11:14] Again the only way to get good at this is to practice....notice there are multiple work sheets [11:14] I thought it said in the book and in the handouts that "anti-Markovnikov" is only with HBr, peroxides [11:15] also make sure you do all of the homework problems at least twice [11:15] and not HCl [11:15] and when preparing for the exam make sure you can do the homework and work sheets WITHOUT NOTES [11:15] on the Addition of carbenes and epoxidation reactions. They come from ch. 13, so will there be questions coming from those as well? [11:16] I think the homework has an example with HCl and peroxides as well..... [11:16] Yes Addition of carbenes and formation of epoxides are from "Reactions of Alkenes" [11:17] Page 331: "the presence or absence of peroxides has no effect on the orentation of addition of hydrogen chloride" [11:17] Use your Study Guides, they have a complete list for exam preparation [11:18] Bring all of the work sheets to class tomorrow for sure [11:19] Please make sure you can complete the work sheets and homework without notes before the exam otherwise you will not "really" be prepared [11:21] So questions? [11:22] Rearangement sare possible with adition of hydrogen halides right [11:23] Yes [11:24] There are multiple examples of rearrangements both in the homework and on the wrok sheets so if you get an incorrect answer go back and chekc for rearrangements... [11:26] Ok, and I'm still a little thrown by what you just said aboutHCl with peroxides being Ani-Markovnikov because in your handouts on slide #17 it says "Ani-Markovnikov" orentation note: only for HBr and in the book it says Page 331: "the presence or absence of peroxides has no effect on the orentation of addition of hydrogen chloride" [11:27] * Michele has quit IRC (Ping timeout: 240 seconds) [11:27] Just HBr [11:28] ok, I must have just misunderstood you... [11:28] * Shelley has quit IRC (Quit: Leaving) [11:29] So I'll see you all tomorrow [11:29] * DrSturm has quit IRC [11:29] * jicra1 has quit IRC (Quit: Leaving) [11:29] * freddy has quit IRC (Quit: Leaving) [11:29] * bn has quit IRC (Quit: Leaving) [11:29] * Disconnected Session Close: Mon Jun 15 11:29:36 2009