即 an-2 =4an+| -4an.所以 an+2 -2an.| =2(an.| -2an) 又由已知条件知, (I_1=1 ,S3 =a1 +a2 =4a1 +2.计算得 (l_2=5 。令 bn=an.1-2an.则 bn _1=2b n.b1=a2-2a1=3.所以数列{bn}是以3 为首项,2 为公比的等比数列,从而 b_n=3*2^(n-1) .即 an.1-2an=...
F138bn=3×21提示:既然bn=a+1-2an则b1=a2-2a1=5-2×1=3(a2可令条件式n=1求出),bn+1=an+2-2a+1.考虑到bn只与an有关,故条件式中Sn多余,设法消去(这句台词是不是耳朵都听起茧子啦?没错,多写真题就会发现:真题是不断重复的,这才是高考真题的真相)观察:Sn+1=4an+2①,当n≥2时,有S...
近日,哈佛大学Eric N. Jacobsen(通讯作者)课题组在Nature上发表了题为“Quaternary stereocentres via an enantioconvergent catalytic SN1 reaction” 的文章。报告了SN1型反应机理的不对称催化作用,导致了由外消旋前体对映选择性构建四元立体中心。 该转化依赖于手性氢键给体催化剂与强路易斯酸促进剂的协同作用,以介导...
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ANTIVIRAL ACTIVITIES OF 4′‐(9‐ACRIDINYLAMINO)‐METHANESULFON‐M‐ANISIDE (SN11841)doi:10.1111/j.1749-6632.1977.tb21982.xDaniel M ByrdDepartment of Pharmacology University of Oklahoma College of Medicine Oklahoma CityOklahoma 73190Annals of the New York Academy of Sciences...
1)因为 Sn.1 =Sn+an+1(nEN'),所以 Sn.1-Sn=an+1.即an.1=an+1.所以an. -a.= 所以|an}是以 a_1=1 为首项,} 为公差的等差数列,所以 a_(tr)=u , 设正项等比数列bn}的公比为q(q0),由 b_2b_4=b_1^2=1 ,解得 b_3=1 , 又、是1 2 6,与5b、的等差中项,所以 12b_1...
A.-4 B.-2 C. 2 D. 4 相关知识点: 试题来源: 解析 答案见上8.A 解析:S .S .S 成等差数列 ∴2Sn=S3+S . ∴(S S )+(Sn-S4)=0, (a_i+a_s+a_i)+(a_i+a_(si)+a_i)+(a_(ij)+a_i) 即(a7+as+an)+(a7 an )=0. ∴2(a_1+a_1+a_1+a_1+a_1+a_1+a_1+a...
Exercise ameliorates chronic inflammatory response induced by high-fat diet via Sestrin2 in an Nrf2-dependent manner Authors - Sujuan Liu View Article human WB,IHC Osteoarthritis Cartilage Suppression of Sestrins in aging and osteoarthritic cartilage: dysfunction of an important stress defense mechanism....
Here is a list of some more bulky bases thatsomeprofessors like to use. Be aware that this is not a comprehensive list! You may also see NaNH2and NaH (small, non-nucleophilic bases) react via an E2for primary leaving groups, so keep that in mind!
The difference between SN1 and SN2 reaction with example: In an SN1 reaction, 2-bromo-2-methylpropane reacts via a carbocation intermediate, while in an SN2 reaction, methyl chloride reacts with hydroxide in a single step. 6. Can you explain the difference between SN1 and SN2? The differ...