化學RESONANCE/HYPERCONJUCATION

我想問下呢2者有無分別???

Update:

明白了,謝謝

Update 2:

如果係ALKENE,有ALKYL GROUP係C,C DOUBLE BOND旁邊,ALKYL GROUP同個C就會有P ORBITAL OVERLAP,咁D ELECTRON會MORE DISPERSE,會STABLE D,但係ALKYL GROUP 有POSITIVE INDUCTIVE EFFECT,D ELECTRON 會推左去DOUBLE BOND果度,佢唔係應該更加REACTIVE咩?

Update 3:

F.7,見到參考書上有呢個字,搞到我唔明= =

Update 4:

嗯嗯,我都問左老師,大約佢解都同你差唔多意思,佢話D ALKYL GROUP係用黎做HYPERCONJUCATION,令到本身個REACTANT STABLE D,而且係CARBOCATION果時,因為ALKYL GROUP 有POSITIVE INDUCTIVE EFFECT,D ELECTRON 推去+位置,令到個INTERMEDIATE更加STABLE,所以ACTIVATION ENERGY 低左,大約係佢本身又STABLE,而且去到INTERMEDIATE又STABLE 的意思吧

Update 5:

唔使客氣^^大家都學到野

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    Resonance/hyperconjucation 我想問下呢2者有無分別???

    Ans:

    兩者有好大分別,係兩樣完全唔同既concept

    1)

    Resonance 係表示分子結構既一種方法,對一D 唔可以用一個Lewis structure黎表達既分子、離子或者自由基,用幾個Lewis structure既共振黎表達佢既結構。

    簡單D講,即係有一個唔準確地知佢Lewis structure 既分子,我地就列哂佢所有可能既Lewis structures出黎。

    最常用既例子係benzene,

    圖片參考:http://imgcld.yimg.com/8/n/HA00656648/o/7011092300...

    由幅圖見到D double bond 既位置唔能夠準確咁知到(因為D delocalized electons 系carbon ring度走黎走去),所以就畫哂兩個可能既Lewis strutures 出黎,呢兩個Lewis strutures 就係叫做resonance.

    2)

    Hyperconjucation,係interaction of the electrons in a sigma bond (usually C–H or C–C) with "an adjacent empty (or partially filled) non-bonding p-orbrital or antibonding pi orbital or filled π orbital", to give an extended molecular orbital that increases the stability of the system

    即係話,由於sigma bond 入面既electron 同隔黎既野(睇英文"...",唔想打多次)相互作用,比出一個更穩定既system.

    最常用既例子係carbocation :

    由於C-C sigma bond 可以轉動,佢另外三個 C-H bond 就undergo 呢個stablize 既interaction,所以就可以得出

    Carbocations 既 stability 係

    (CH3)3C(+) > (CH3)2CH(+) > (CH3)CH2(+) > CH3(+)

    呢個既concept 比較深,唔知你明唔明;唔明可以再問。

    黑白灰_唯物主義者

    2011-09-27 19:27:29 補充:

    可唔可以話比我聽,你讀緊咩課程(CE?AL?AS?DSE?定其他?) 同讀緊咩topic,因為我唔知點答你。

    如果你讀緊U 我幫你唔到,我F.5 咋。

    2011-09-30 00:24:56 補充:

    以下係個人想法,唔知岩唔岩

    1) in alkyl group, 個C undergo sp3 hybridization(唔知你有無聽過呢樣野),而double bond 個C 就undergo sp2 hybridization.

    即係 alkyl group 個C 有四個form 左sigma-bond 既sp3 orbital;double bond 個C有 一個form 左pi-bond 既pz orbital 同三個form 左sigma-bond 既sp2 orbital。

    所以,我諗應該無p-orbital overlap。

    2011-09-30 00:25:27 補充:

    2) 我問左我個老師,佢話alkyl group 個 positive inductive effect係用黎比較唔同carbocation(1度、2度、3度)同H 既energetic stability。

    同埋,我上網搵左,佢話alkyl group 有electron donating nature,而且係towards 個double bond (即係你講既推去double bond),但係咁係會 **stabilize** 個alkene 同埋令佢有dipole moment。

    至於原因,我唔知,佢亦都無explain。

    以下係我估既:

    2011-09-30 00:29:42 補充:

    (i)

    **假設**因某D 原因令alkene 駁去alkyl group 既bond, homolytic fission左,形成 @ 同 alkyl group #

    (ii)

    Reaction 既開始就係 @ + #

    由於 # 非常非常reactive,同埋@,理論上都係非常非常reactive, # 就會同 @ react 得好勁。

    2011-09-30 00:29:48 補充:

    (iii)

    由於 # 有electron donating nature,佢會推electron 去 @ 既double bond度,令 自己同 @ 都stable D

    咁就會形成一個相對地非常唔reactive 既alkene,即係一個low energy 同stable D 既alkene。

    2011-10-03 16:43:16 補充:

    哦... 原來係咁,多謝你講番比我聽,THX!~

    Source(s): 黑白灰_唯物主義者
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